Note that PT_GETREGS supplies SSTATUS for FreeBSD/riscv.

Note that PT_GETREGS supplies SSTATUS for FreeBSD/riscv.

This permits reading the value of the SSTATUS CSR returned by ptrace()
for live FreeBSD/riscv processes.

	* riscv-fbsd-nat.c (getregs_supplies): Return true for
	RISCV_CSR_SSTATUS_REGNUM.