libosmogb is an anomaly since it has its headers in osmocom/gprs
directory instead of osmocom/gb. This is really confusing for users.
Furthermore, libosmo-gprs is also using osmocom/gprs, which will create
even more confusion.
This patch moves all existing osmocom/gprs/ header files under
osmocom/gb/ directory (except the backward-compat ones which were
added pointing to the ones in osmocom/gsm/).
Next, new files are added in osmocom/gprs/ replacing the ones that used
to be tehre, with a pragma message announcing deprecating and asking
users to use the new path instead.
This allows keeping old applications working, while announcing
deprecation of the old osmocom/gprs/ patch and have all new development
happen under osmocom/gb/.
Change-Id: I6e826775552766e34e4c06fe2390084596dfc286
