power: qpnp-fg-gen4: Enable mem-attn interrupt dynamically

Currently, mem-attn interrupt is used for signalling when the
parallel summing measurement configuration needs to be changed.
Since this interrupt is kept enabled when the device is active,
it brings in power penalty. Enable this interrupt dynamically
when the parallel current summing configuration needs to be
changed and disable it once that is done. This helps with power
savings.

Change-Id: I663cab1cb89b69427dc996bbefae16cf8b1f80a3
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>