bcm2835: new package

[Thomas:
 - addition of 'depends on BR2_arm' as suggested by Yann.
 - addition of a comment in the Config.in help text that says that
   this library is a pure abomination.
 - fix the hash, since apparently upstream changes the released
   tarballs after they are published.
 - fix license, it's GPLv2, not GPLv2+.]

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>