Hexagon (tests/tcg/hexagon) fix inline asm in preg_alias.c

Replace consecutive inline asm blocks with a single one with proper
outputs/inputs/clobbers rather than making assumptions about register
values being carried between separate blocks.

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20220210021556.9217-10-tsimpson@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>