[ARM] 4567/1: Fix 'Oops - undefined instruction' when CONFIG_VFP=y on non VFP device

vfp_init() takes care of the condition when CONFIG_VFP=y but no real VFP
device exists. However, when this condition is true, a compiler might
misplace code lines in a way that will break this support. (To be more
specific - fmrx(FPSID) might be executed before vfp_testing_entry
assignment, which will end up with Oops - undefined instruction).
This patch adds a barrier() to guarantee the right execution ordering.

Signed-off-by: Assaf Hoffman
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>