target/riscv: Fix vcompress with rvv_ta_all_1s

target/riscv: Fix vcompress with rvv_ta_all_1s

vcompress packs vl or less fields into vd, so the tail starts after the
last packed field. This could be more clearly expressed in the ISA,
but for now this thread helps to explain it:

https://github.com/riscv/riscv-v-spec/issues/796

Signed-off-by: Anton Blanchard <antonb@tenstorrent.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241030043538.939712-1-antonb@tenstorrent.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>