clk: qcom: gdsc: Add support to enable retention of GSDCR

Add support for the RETAIN_FF_ENABLE feature which enables the
usage of retention registers. These registers maintain their
state after disabling and re-enabling a GDSC.

Signed-off-by: Taniya Das <tdas@codeaurora.org>
Link: https://lore.kernel.org/r/1595606878-2664-2-git-send-email-tdas@codeaurora.org


Signed-off-by: Stephen Boyd <sboyd@kernel.org>