Add ARM support into xf86drm.h

This provides support for Xorg interface. Without this the vivante samples will hang during close requiring a reboot

[Adapted from yocto project] Upstream-Status: Pending Signed-off-by: Lauren Post lauren.post@freescale.com Signed-off-by: Evan Kotara evan.kotara@freescale.com [Thomas: change CAS code to only be used on ARMv6/ARMv7, and not ARMv4/ARMv5, which don't support ldrex/strex. If no CAS implementation is provided libdrm falls back to a system call for locking/unlocking.] Signed-off-by: Thomas Petazzoni thomas.petazzoni@free-electrons.com Signed-off-by: Peter Seiderer ps.report@gmx.net