target/arm: Update arm_sctlr for VHE

target/arm: Update arm_sctlr for VHE

Use the correct sctlr for EL2&0 regime.  Due to header ordering,
and where arm_mmu_idx_el is declared, we need to move the function
out of line.  Use the function in many more places in order to
select the correct control.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200206105448.4726-23-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>