ART-tests: Remove DX-dependency from 551-checker-shifter-operand

The merging of shift and add operations into DataProcWithShifterOp
in the test case $opt$validateShiftLongAsserts was dependent on
register-allocation patterns. With D8 sometimes the merge did not
take place because the result of the shift was not overwritten by
the subsequent add.

This CL separates the intermittent method calls and the arithmetic
operations so the environmental uses of the shift result does not
block merging. Also, D8 is enabled.

Test: art/test.py -r -b --target -t 551-checker-shifter-operand
      Tested locally with --host and --gcstress.

Bug: 65168732
Change-Id: I3a8e71f3530211878879faae068acb7c7957ae19
2 files changed