g2d: fix using virt_to_phys against stack variable

g2d: fix using virt_to_phys against stack variable

If CONFIG_VMAP_STACK is enabled, kernel stack is not physically linear
any more. Instead, it is allocated from vmap area and virt_to_phys and
similar macros are not available on that area.

G2D driver needs to get phyical address of a structure that describes
job properties to deliver the information to the secure world if G2D
H/W is not capable of protecting secure content leak.

Instead allocating the descriptor from the kernel stack, it is now
placed in g2d_task. It helps reducing data redundancy because all
values of the descriptor are also stored in g2d_task.

Change-Id: I91f9c9c5f3806890b4625db87e8b01627d58e5a0
Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>