Changes for Aoson M12 (Ver.A. with 512MB) including:
 - Defconfig for working audio, touchscreen, wifi, battery
 - Working gsensor probe and correct rotation parameters
 - Correct rotation for camera
 - LCD specs as per datasheet
 - Menu buttons fix: credit to FENISU
Optimise RAM for Aoson 512MB, mostly trial and error but more free RAM available and much smoother. May also work for other 512MB tablets but not tested.
Notes:
 - VPU pmem tweaked to min for playing 1080p (OK i_am_legend clips from www.h264info.com with no errors)
 - UI pmem tweaked to min for no UI crashes in lockscreen + Chrome
 - GPU pmem tweaked to 16MB - somewhat arbitrary but little effect in Antutu score
Some minor possible tidying up:
 - mma8452 debug messages were swamping dmesg
 - earlysuspend for mma8452 was commented out but seems to work
 - 2nd camera was fixed instead of reading from defconfig so added reference to bcam (works for Aoson M12v512MB but can't test on other tabs)
Added long-press volume controls to buttons