msm: footswitch-8x60: Collapse core memory during core power-collapse

Even when a core's power is collapsed, memory within the core remains
powered. Call the clk_set_flags(CLKFLAG_NORETAIN) API from the clock
driver to allow the core memory to collapse when the core clock is
disabled as part of the footswitch collapse sequence. Also re-nable
the retention mode as part of the restore sequence.

CRs-Fixed: 322181
Change-Id: I8e73654d2de0ff108c6579b94700c80ddba186e4
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>