RISC-V: Disable the CSR checking by default.

Add new .option `csr-check/no-csr-check` and GAS option `-mcsr-check
/-mno-csr-check` to enbale/disable the CSR checking.  Disable the CSR
checking by default.

	gas/
	* config/tc-riscv.c: Add new .option and GAS options to enbale/disable
	the CSR checking.  We disable the CSR checking by default.
	(reg_lookup_internal): Check the `riscv_opts.csr_check`
	before we doing the CSR checking.

	* doc/c-riscv.texi: Add description for the new .option and assembler
	options.

	* testsuite/gas/riscv/priv-reg-fail-fext.d: Add `-mcsr-check` to enable
	the CSR checking.
	* testsuite/gas/riscv/priv-reg-fail-rv32-only.d: Likewise.

1 files changed, 13 insertions, 0 deletions

diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index 739670f..599b5cf 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -73,6 +73,15 @@ specification.
 Don't generate the default riscv elf attribute section if the .attribute
 directives are not set.
 
+@cindex @samp{-mcsr-check} option, RISC-V
+@item -mcsr-check
+Enable the CSR checking for the ISA-dependent CRS and the read-only CSR.
+The ISA-dependent CSR are only valid when the specific ISA is set.  The
+read-only CSR can not be written by the CSR instructions.
+
+@cindex @samp{-mno-csr-check} option, RISC-V
+@item -mno-csr-check
+Don't do CSR cheching.
 @end table
 @c man end
 
@@ -174,6 +183,10 @@ opportunistically relax some code sequences, but sometimes this behavior is not
 desirable.
 @end table
 
+@item csr-check
+@itemx no-csr-check
+Enables or disables the CSR checking.
+
 @cindex INSN directives
 @item .insn @var{value}
 @itemx .insn @var{value}