target/arm: Remove redundant mmu_idx lookup

We already have the full ARMMMUIdx as computed from the
function parameter.

For the purpose of regime_has_2_ranges, we can ignore any
difference between AccType_Normal and AccType_Unpriv, which
would be the only difference between the passed mmu_idx
and arm_mmu_idx_el.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-id: 20201008162155.161886-2-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>