aarch64: Mark PMSIDR_EL1 as read-only

We were incorrectly allowing writes to PMSIDR_EL1, which is
a read-only register.
[https://developer.arm.com/documentation/ddi0595/2021-09/AArch64-Registers/PMSIDR-EL1--Sampling-Profiling-ID-Register?lang=en]

opcodes/
	* aarch64-opc.c (aarch64_sys_regs): Make pmsidr_el1 as F_REG_READ.

gas/
	* testsuite/gas/aarch64/msr.s: Remove write to pmsidr_el1.
	* testsuite/gas/aarch64/msr.d: Update accordingly.
	* testsuite/gas/aarch64/illegal-sysreg-2.s,
	* testsuite/gas/aarch64/illegal-sysreg-2.d,
	* testsuite/gas/aarch64/illegal-sysreg-2.l: New test.