target/riscv: rvv-1.0: rename r2_zimm to r2_zimm11

target/riscv: rvv-1.0: rename r2_zimm to r2_zimm11

Rename r2_zimm to r2_zimm11 for the upcoming vsetivli instruction.
vsetivli has 10-bits of zimm but vsetvli has 11-bits of zimm.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-72-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>