scsi: libcxgbi: Use kvzalloc instead of opencoded kzalloc/vzalloc

Remove cxgbi_alloc_big_mem(), cxgbi_free_big_mem() functions and use
kvzalloc/kvfree instead. __GFP_NOWARN added to kvzalloc() call because we
already print a warning in case of allocation fail.

Link: https://lore.kernel.org/r/20200801133123.61834-1-efremov@linux.com


Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>