gpio: msm: Make msmgpio a platform device

The gpio driver was not a true platform driver and hence wasn't
supported by device tree. This patch fixes that for non-DT targets
by making sure the device gets added early on during board init.
For DT-targets, adding the gpio-controller property for the device
makes sure the msmgpio device gets probed.
This change is done for all TLMM_v2 targets (msm8660 and future)
TLMM_V1 targets remain unaffected.

Change-Id: I8a55ab1e2af0366b3e6893b334ba2396d2a83190
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>