RISC-V: PR28733, add missing extension info to 'invalid CSR' error

RISC-V: PR28733, add missing extension info to 'invalid CSR' error

Currently we report errors as "invalid CSR 'fscr' for the current ISA"
when the instruction isn't valid.

This patch expands that error message to include the missing extension
information. For example, now the error message would be "invalid CSR
'fscr' for the current ISA, CSR 'fscr' needs 'f' extension".

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>
gas/
	pr 28733
	* config/tc-riscv.c (riscv_csr_address): Report more details
	when the CSR is invalid.
	* testsuite/gas/riscv/csr-version-1p10.l: Updated detailed errors.
	* testsuite/gas/riscv/csr-version-1p11.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p12.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p9p1.l: Likewise.