testsuite: arm: Relax expected asm in bitfield* and union-2 tests

Below -O2, lsls/lsrs are prefered. For -O2 and above, lsl/lsr are
prefered.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/cmse/mainline/8_1m/bitfield-4.c: Allow lsl and
	lsr instructions.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-6.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-and-union.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/union-2.c: Likewise.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>