testsuite, X86: Where scan-asm tests depend on 'generic' tuning, use it.

The follwoing tests pass or fail depending on the --with-cpu= configuration
of the platform, since that sets the default tuning.  They require 'generic'
tuning to work reliably in such cases, so make that explicit.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512bw-pr103750-2.c: Add -mtune=generic.
	* gcc.target/i386/avx512bw-pr88465.c: Likewise.
	* gcc.target/i386/avx512dq-pr88465.c: Likewise.
	* gcc.target/i386/avx512f-pr103750-2.c: Likewise.
	* gcc.target/i386/avx512f-pr88465.c: Likewise.
	* gcc.target/i386/avx512fp16-pr103750-2.c: Likewise.
	* gcc.target/i386/sse2-stv-2.c: Likewise.
	* gcc.target/i386/sse2-stv-3.c: Likewise.
	* gcc.target/i386/sse2-stv-4.c: Likewise.
	* gcc.target/i386/sse2-stv-5.c: Likewise.
	* gcc.target/i386/sse2-stv-6.c: Likewise.
	* gcc.target/i386/sse2-stv-7.c: Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>