ENGR00212489-1 viv_GPU: add reserved memory account handler.

ENGR00212489-1 viv_GPU: add reserved memory account handler.

the original low memory killer only take care of system memory accounting,
but for so large shared memory occupy by GPU, and each process memory
killer account become unfair, very large 3D game will not killed firstly
if it going to background.

Add this account to let real large memory user get killed if going to background
eg, the "angry bird Space" will acquire 68,215,360 GPU memory for 1-6 toll-gate.

The test show it can quicker recovery from memory shortage situation,
since it's very like to be killed after add so much GPU memory for such 3D game.

Signed-off-by: Zhang Jiejing <jiejing.zhang@freescale.com>