An old comment in get_phys_addr_lpae() claims that the code does not
support the different format TCR for VTCR_EL2.  This used to be true
but it is not true now (in particular the aa64_va_parameters() and
aa32_va_parameters() functions correctly handle the different
register format by checking whether the mmu_idx is Stage2).
Remove the out of date parts of the comment.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200331143407.3186-1-peter.maydell@linaro.org