Append ".p2align 4,0" to i386 assembler tests to support mingw targets.

	* testsuite/gas/i386/avx512f-plain.s: Append ".p2align 4,0".
	* testsuite/gas/i386/avx512vl-plain.s: Likewise.
	* testsuite/gas/i386/bnd.s: Likewise.
	* testsuite/gas/i386/stN.s: Likewise.
	* testsuite/gas/i386/avx512f-plain.l: Updated.
	* testsuite/gas/i386/avx512vl-plain.l: Likewise.
	* testsuite/gas/i386/bnd.l: Likewise.
	* testsuite/gas/i386/stN.l: Likewise.