msm: kgsl: Allocate physical pages instead of using vmalloc

Replace vmalloc allocation with physical page allocation. For most
allocations we do not need a kernel virual address. vmalloc uses up
the kernel virtual address space. By replacing vmalloc with physical
page alloction and mapping that allocation to kernel space only
when it is required prevents the kgsl driver from using unnecessary
vmalloc virtual space.

Change-Id: Idc716c8366f837f06a61b154deacec65a3a0662e
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>