[SCSI] imm: no need for unchecked_isa_dma

Relax the lowmem bounce buffer requirement for imm so that any
low memory page will do -- they don't need to be below the
ISA 16 MB limit, just need to be mapped in low memory.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>