msm: kgsl: Remove tracking virtual map sizes

mmapsize is no longer important to the memory descriptor
and the APIs that would use it never materialized. It currently
just tracks the size of the memdesc and is no longer needed.

Change-Id: I8fa1001c2f89f23034029de7de6ab77532bf45fa
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>