Add half support for AVX512 register view.

Add half support for AVX512 register view.

This adds support for the half datatype, FP16, to the AVX512 register printing.

gdb/ChangeLog:
2020-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* i386-tdep.c (i386_zmm_type) <v32_half>: New field.
	(i386_ymm_type) <v16_half>: New field.
	(i386_gdbarch_init): Add set_gdbarch_half_format.
	* features/i386/64bit-avx512.xml: Add half type.
	* features/i386/64bit-avx512.c: Regenerated.
	* features/i386/64bit-sse.xml: Add half type.
	* features/i386/64bit-sse.c: Regenerated.

gdb/testsuite/ChangeLog:
2021-07-21  Felix Willgerodt  <Felix.Willgerodt@intel.com>

	* gdb.arch/x86-avx512fp16.c: New file.
	* gdb.arch/x86-avx512fp16.exp: New file.
	* lib/gdb.exp (skip_avx512fp16_tests): New function.