target/riscv: Add support to access ctrsource, ctrtarget, ctrdata regs.

target/riscv: Add support to access ctrsource, ctrtarget, ctrdata regs.

CTR entries are accessed using ctrsource, ctrtarget and ctrdata
registers using smcsrind/sscsrind extension. This commits extends
the csrind extension to support CTR registers.

ctrsource is accessible through xireg CSR, ctrtarget is accessible
through xireg1 and ctrdata is accessible through xireg2 CSR.

CTR supports maximum depth of 256 entries which are accessed using
xiselect range 0x200 to 0x2ff.

This commits also adds properties to enable CTR extension. CTR can be
enabled using smctr=true and ssctr=true now.

Signed-off-by: Rajnesh Kanwal <rkanwal@rivosinc.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250212-b4-ctr_upstream_v6-v7-1-4e8159ea33bf@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>