clean-up pkg-config files: Make use of "Requires" as documented

According to the pkg-config manual, "Libs" should not contain flags
for _required_ packages.  Instead, they should be expressed via
"Requires".  Let's do that

Change-Id: I2ab1fe8e4bbfc120b471d6c9f2312a89dbc7d42b

libosmocodec.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom Codec related utilities Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmocodec
-Cflags: -I${includedir}/ @TALLOC_CFLAGS@
-
+Requires: talloc, libosmocore
+Libs: -L${libdir} -losmocodec
+Cflags: -I${includedir}/

libosmocoding.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom L1 transcoding Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmocoding -losmocodec -losmogsm -losmocore
-Cflags: -I${includedir}/ @TALLOC_CFLAGS@
-
+Requires: talloc, libosmocore, libosmogsm, libosmocodec
+Libs: -L${libdir} -losmocoding
+Cflags: -I${includedir}/

libosmocore.pc.in

@@ -6,6 +6,7 @@ includedir=@includedir@
 Name: Osmocom Core Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmocore
-Libs.private: @PTHREAD_LIBS@ @LIBSCTP_LIBS@
-Cflags: -I${includedir}/ @TALLOC_CFLAGS@ @PTHREAD_CFLAGS@
+Requires: talloc, libsctp
+Libs: -L${libdir} -losmocore
+Libs.private: @PTHREAD_LIBS@
+Cflags: -I${includedir}/ @PTHREAD_CFLAGS@

libosmoctrl.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom Control Interface Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmoctrl -losmogsm -losmocore
+Requires: talloc, libosmocore, libosmogsm
+Libs: -L${libdir} -losmoctrl
 Cflags: -I${includedir}/
-

libosmogb.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom GPRS Gb Library
 Description: Osmocom GPRS Gb Interface (NS/BSSGP) Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmogb -losmovty -losmocore
+Requires: libosmocore, libosmovty
+Libs: -L${libdir} -losmogb
 Cflags: -I${includedir}/ -fno-strict-aliasing
-

libosmogsm.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom GSM Core Library
 Description: GSM Core Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmogsm -losmocore
+Requires: talloc, libosmocore
+Libs: -L${libdir} -losmogsm
 Cflags: -I${includedir}/
-

libosmosim.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom SIM card related utilities Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmosim -losmocore
+Requires: talloc, libosmocore
+Libs: -L${libdir} -losmosim
 Cflags: -I${includedir}/
-

libosmousb.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom libusb (USB) integration
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmousb -losmocore
+Requires: talloc, libusb-1.0, libosmocore
+Libs: -L${libdir} -losmousb
 Cflags: -I${includedir}/
-

libosmovty.pc.in

@@ -6,6 +6,6 @@ includedir=@includedir@
 Name: Osmocom VTY Interface Library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @TALLOC_LIBS@ -losmovty -losmocore
+Requires: libosmocore
+Libs: -L${libdir} -losmovty
 Cflags: -I${includedir}/
-