[XCVmem] Normal register-immediate store not recognized

Created by: MaryBennett

For example:

(set
  (mem:SI
    (plus:SI
      (reg/f:SI 136 [ _8 ])
      (reg:SI 140 [ivtmp.70 ]))
    [ 1 MEM[(int *)_8 + ivtmp.70_3 * 1]+0 S4 A32])
  (const_int 0 [0]))