msm : kgsl: Fix clk_unprepare() ref count issue

During low power states of NAP and DEEP_NAP,
driver has to perform clk_enable() and return.
But in the current code, driver is performing
clk_prepare_enable() in DEEP_NAP state, which is
causing ref count issue for clk_uprepare thus
graphics clocks voting for XO and preventing XO
shutdown. Fixed this by adding DEEP_NAP check to
perform only clk_enable, similar to NAP state.

CRs-fixed: 2081825
Change-Id: I465c9aea2ba876fa488e2f665a762e8e4c50b0fd
Signed-off-by: Archana Sriram <apsrir@codeaurora.org>