scsi: mpt3sas: Remove CPU arch check to determine perf_mode

Currently default perf_mode is set to 'balanced' on Intel architecture
machines and on other machines default perf_mode is set to 'latency' mode.

This CPU architecture check is removed and the default perf_mode mode is
set to 'balanced' mode on all machines.

User can choose the required performance mode using perf_mode module
parameter.

Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>