power: fg-memif: Wait before polling MEM_GNT first time

Currently, MEM_GNT bit is polled immediately after requesting
DMA. Some times it is not set while polling for the first time
adding a wait time of 10 ms every SRAM transaction. Hardware
takes 5 cycles (25 us) of 200 KHz clock to respond to the
request. Add a delay of 40 us before polling MEM_GNT first time
to improve the latency seen with SRAM transactions.

CRs-Fixed: 2151239
Change-Id: Ic26f1380194c20544ed9fc9ea0459afa29d98b09
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>