target/riscv: rvv: speed up small unit-stride loads and stores

target/riscv: rvv: speed up small unit-stride loads and stores

Calling `vext_continuous_ldst_tlb` for load/stores up to 6 bytes
significantly improves performance.

Co-authored-by: Helene CHELIN <helene.chelin@embecosm.com>
Co-authored-by: Paolo Savini <paolo.savini@embecosm.com>
Co-authored-by: Craig Blackmore <craig.blackmore@embecosm.com>
Signed-off-by: Helene CHELIN <helene.chelin@embecosm.com>
Signed-off-by: Paolo Savini <paolo.savini@embecosm.com>
Signed-off-by: Craig Blackmore <craig.blackmore@embecosm.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20241218142353.1027938-3-craig.blackmore@embecosm.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>