Hexagon (target/hexagon) cleanup gen_store_conditional[48] functions

Previously the store-conditional code was writing to hex_pred[prednum].
Then, the fGEN_TCG override was reading from there to the destination
variable so that the packet commit logic would handle it properly.

The correct implementation is to write to the destination variable
and don't have the extra read in the override.

Remove the unused arguments from gen_store_conditional[48]

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <1622589584-22571-4-git-send-email-tsimpson@quicinc.com>