[PATCH, BINUTILS, AARCH64, 6/9] Add Random number instructions

[PATCH, BINUTILS, AARCH64, 6/9] Add Random number instructions

This patch is part of the patch series to add support for ARMv8.5-A
extensions.
(https://developer.arm.com/products/architecture/cpu-architecture/a-profile/exploration-tools)
The encodings can be found in the System Register XML.

This patch adds the following:
MSR Xn, RNDR
MSR Xn, RNDRRS

These are optional instructions in ARMv8.5-A and hence the new
+rng is added.

*** include/ChangeLog ***

2018-10-09  Sudakshina Das  <sudi.das@arm.com>

	* opcode/aarch64.h (AARCH64_FEATURE_RNG): New.

*** opcodes/ChangeLog ***

2018-10-09  Sudakshina Das  <sudi.das@arm.com>

	* aarch64-opc.c (aarch64_sys_regs): New entries for
	rndr and rndrrs.
	(aarch64_sys_reg_supported_p): New check for above.

*** gas/ChangeLog ***

2018-10-09  Sudakshina Das  <sudi.das@arm.com>

	* config/tc-aarch64.c (aarch64_features): New "rng" option.
	* doc/c-aarch64.texi: Document the same.
	* testsuite/gas/aarch64/sysreg-4.s: Test both instructions.
	* testsuite/gas/aarch64/sysreg-4.d: Likewise.
	* testsuite/gas/aarch64/illegal-sysreg-4.l: Likewise.