msm: kgsl: Move GMU to a component device

Traditionally the GMU/RGMU device has been a child of the adreno device
and probed manually. That has worked despite the fact that the GMU/RGMU
device has resources of its own and it really should be a top level
platform device.

Finally do the right thing, make GMU a top level platform device and
driver and bind it to Adreno as a component. This will make sure we
get the advantages of all of the platform level initialization without
having to code in half a dozen hacks to make everything work and then
break again next kernel version.

Change-Id: Ic0dedbadf6776e1a4f5e0eb1e093241e5103b3ff
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>