RISC-V: Updated CSRs to privileged spec v1.12 and debug spec v1.0.

* Removed N extension CSRs,
ustatus, uie, utvec, uscratch, uepc, ucause, utval and uip.

* Removed two supervisor CSRs,
sedeleg and sideleg.

* Changed debug CSR address of scontext from 0x7aa to 0x5a8.  We cannot support
different versions of debug specs for now, so only supporting the latest one is
the only way to move forward.

* Added debug CSRs,
mscontext (0x7aa), mcontrol6 (0x7a1, tdata1) and tmexttrigger ((0x7a1, tdata1).

* Regarded hcontext as a debug CSR.

include/
	* opcode/riscv-opc.h: Updated CSRs to privileged spec v1.12 and
	debug spec v1.0.
gas/
	* testsuite/gas/riscv/csr.s: Updated CSRs to privileged spec v1.12
	and debug spec v1.0.
	* testsuite/gas/riscv/csr-dw-regnums.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p10.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p10.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p11.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p11.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p12.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p12.l: Likewise.
	* testsuite/gas/riscv/csr-version-1p9p1.d: Likewise.
	* testsuite/gas/riscv/csr-version-1p9p1.l: Likewise.
	* testsuite/gas/riscv/csr-dw-regnums.d: Likewise.
	* testsuite/gas/riscv/csr-dw-regnums.s: Likewise.