msm: kgsl: Move kgsl_pool_allocate_pages()

For reasons unknown while most of the pool code was properly living in
kgsl_pool.c, kgsl_pool_allocate_pages() was in kgsl_sharedmem.c and
depended on several other exported functions just to make it work.  Move
the function and fix up the helper functions.

Change-Id: Ic0dedbad7a7c06adce4f87f7915853eb44a4151c
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>