msm: kgsl: remove *MMU type options from Kconfig

Remove the ability to switch between gpummu and iommu via
kernel config. The new decision path is: if kgsl.mmutype is set,
use that. Otherwise if iommu_found() use iommu, and last
but not least use the gpummu.

Change-Id: I6d34baf72da53e566bfa7081c6741f7fd0180aea
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>