target/ppc/mem_helper.c: Remove a conditional from dcbz_common()

target/ppc/mem_helper.c: Remove a conditional from dcbz_common()

Instead of passing a bool and select a value within dcbz_common() let
the callers pass in the right value to avoid this conditional
statement. On PPC dcbz is often used to zero memory and some code uses
it a lot. This change improves the run time of a test case that copies
memory with a dcbz call in every iteration from 6.23 to 5.83 seconds.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <20240622204833.5F7C74E6000@zero.eik.bme.hu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>