msm: clock-local: Move GFX3D core reset from reg_init() to post_init()

reg_init() is called from the clock driver's pre_init() function, which
runs too early for clock APIs to be safely called. Move the GFX3D reset
operation that was performed there into post_init() where clock APIs
are allowed.

Change-Id: I63f6e9eec508f111ddf4211c63fc317bbe128a27
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>