[SCSI] mpt2sas: Added command line option diag_buffer_enable.

Added command line option diag_buffer_enable. When the command line option is
set, the driver will automatically post diag buffers at driver load time.
The command line option diag_buffer_enable is bitwise, so it's possible to
enable both and/or snapshot + trace buffers.  For trace, the driver will
allocate 1MB buffer, whereas for snapshot its 2MB. The purpose for this is
so the enduser doesn't have to manually use an application to setup diag
buffers for debugging firmware related issues.

Here is some examples
trace:
# insmod mpt2sas.ko diag_buffer_enable=1

snapshot:
# insmod mpt2sas.ko diag_buffer_enable=2

both trace and snapshot:
# insmod mpt2sas.ko diag_buffer_enable=3

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: Eric Moore <Eric.moore@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>