i386: Fix behavior for both using AVX10.1-256 in options and function attribute

When we are using -mavx10.1-256 in command line and avx10.1-256 in
target attribute together, zmm should never be generated. But current
GCC will generate zmm since it wrongly enables EVEX512 for non-explicitly
set AVX512. This patch will fix that issue.

gcc/ChangeLog:

	* config/i386/i386-options.cc (ix86_valid_target_attribute_tree):
	Check whether AVX512F is explicitly enabled.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx10_1-24.c: New test.