RISC-V: Add augmented hypervisor extension 'sha' support.

RISC-V: Add augmented hypervisor extension 'sha' support.

The augmented hypervisor extension 'sha'[1] is a new profile-defined extension
that captures the full set of features that are mandated to be supported along
with the H extension.

https://github.com/riscv/riscv-profiles/blob/main/src/rva23-profile.adoc#rva23s64-profile

bfd/ChangeLog:

		* elfxx-riscv.c: New extension and implies.

gas/ChangeLog:

		* NEWS: New extension.
		* testsuite/gas/riscv/imply.d: New test for sha.
		* testsuite/gas/riscv/imply.s: Ditto.
		* testsuite/gas/riscv/march-help.l: New extension.