msm: clock-8x60: Allow setting of memory retention modes

Similar to the recent 8960 changes, add support for setting the
memory retention bits associated with some multimedia clocks.

By default, core memory is left powered and retained when the
clock is halted. This setting can now be changed using the
clk_set_flags() API to save power when memory contents can be
sacrificed.

Change-Id: I1f2da26e1ebb6acc10ec8d3022c2247fa9555672
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>