s390: Fix tests rosbg_si_srl and rxsbg_si_srl

Starting with r14-2047-gd0e891406b16dc two SI mode tests are optimized
into DI mode.  Thus, the scan-assembler directives fail.  For example
RTL expression

(ior:SI (subreg:SI (lshiftrt:DI (reg:DI 69)
            (const_int 2 [0x2])) 4)
    (subreg:SI (reg:DI 68) 4))

is optimized into

(ior:DI (lshiftrt:DI (reg:DI 69)
        (const_int 2 [0x2]))
    (reg:DI 68))

Fixed by moving operands into memory in order to enforce SI mode
computation.

Furthermore, in r9-6056-g290dfd9bc7bea2 the starting bit position of the
scan-assembler directive for rosbg was incorrectly set to 32 which
actually should be 32+SHIFT_AMOUNT, i.e., in this particular case 34.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/md/rXsbg_mode_sXl.c: Fix tests rosbg_si_srl
	and rxsbg_si_srl.