gnupg2: new package

[Thomas: use libpthsem instead of pth, remove !uclibc dependency,
minor formatting fixes in the .mk file.]

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Markos Chandras <Markos.Chandras@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>