msm: kgsl: better handling of virtual address fragmentation

When KGSL_MEMFLAGS_USE_CPU_MAP is enabled, the mmap address
must try to match the GPU alignment requirements of the buffer,
as well as include space in the mapping for the guard page.
This can cause -ENOMEM to be returned from get_unmapped_area()
when there are a large number of mappings. When this happens,
fall back to page alignment and retry to avoid failure.

Change-Id: I2176fe57afc96d8cf1fe1c694836305ddc3c3420
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>