Implement enable_fpu() and disable_fpu().
enable_fpu() disables interrupt and then enables FPU.
disable_fpu() disables FPU and enables interrupt.
Also added a CONFIG_FPU flag.
BUG=chrome-os-partner:7920
TEST=none
Change-Id: I2d71f396d9c7d7ac4a6a2d525f3d86f8aae87521
Signed-off-by: Vic Yang <victoryang@chromium.org>