target/ppc: Use cpu_*_mmuidx_ra instead of MMU_MODE*_SUFFIX

target/ppc: Use cpu_*_mmuidx_ra instead of MMU_MODE*_SUFFIX

There are only two uses.  Within dcbz_common, the local variable
mmu_idx already contains the epid computation, and we can avoid
repeating it for the store.  Within helper_icbiep, the usage is
trivially expanded using PPC_TLB_EPID_LOAD.

Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>