hwc: fix probable typo/thinko

Caught by this gcc warning:

hardware/ti/omap3/hwc/hwc.c: In function 'omap3_hwc_prepare':
hardware/ti/omap3/hwc/hwc.c:1054:31: warning: comparison between pointer and integer [enabled by default]

Change-Id: I1e34ba2e8de960585abe444908204ba5b485f354
hwc: silence a compiler warning

hardware/ti/omap3/hwc/hwc.c: In function 'omap3_hwc_prepare':
hardware/ti/omap3/hwc/hwc.c:1057:49: warning: assignment from incompatible pointer type [enabled by default]

Change-Id: I2f492ef390efeeb8a4ca5f94f1432665179c8eb6
hwc: Fix check for presence of sysfs vsync_time file

Change-Id: Ic3377463a87bd789b712fc688493dfdd7a2b0abd
hwc: allow building in Thumb mode on ARM

On an ARMv7 CPU like the OMAP3, Thumb mode brings a significant
reduction in code size without performance penalty (for that matter, the
reduced code size will reduce icache footprint, probably increasing
performance slightly).

Change-Id: I54ba1361a41f2df7ec3ae9ef7529638a2a18d25d