scsi: ufs: enable FASTAUTO mode during low load condition

We are currently running UFS link in HS-G3 FAST mode during high load
condition for best possible performance and in HS-G2 FAST mode during
low load condition to save power. As we are anyway scaling down from
HS-G3 to HS-G2, we can also change the mode from FAST to FASTAUTO.
So we looked at the performance numbers with HS-G2 FASTAUTO mode and
they are good enough for most of the low bandwidth usecases. But Samsung
UFS memory devices are exception which has really low sequential read
throughput in FAST AUTO mode hence we will only be enabling FAST AUTO mode
for other UFS device vendors.

Change-Id: Ia79da3e82fb87c0e396534979398617388f40af9
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>