power: qpnp-fg-gen4: Use dynamically allocated buffer for SRAM dump

Currently, buffer for dumping SRAM periodically is allocated on
the stack. Dynamically allocate the buffer to reduce stack
footprint.

Change-Id: I35ce52d6520e85a71c6e228b172c01ba4a86619c
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>