msm: kgsl: don't map private entries into all pagetables

Several entries in the global list should only be mapped
into the priv_bank_table. However, they must use the same
address space as the other global entries. So keep them
in the list, but add a memdesc->priv bit to enable
this behavior.

Change-Id: I0239e675bcb39ac84d00ee3903667d7e6dded048
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>