ArmPkg/ArmMmuLib: drop pointless LookupAddresstoRootTable() routine

ArmPkg/ArmMmuLib: drop pointless LookupAddresstoRootTable() routine

LookupAddresstoRootTable() uses a loop to go over its MaxAddress
argument, essentially to do a log2() and determine how many bits are
needed to represent it. Since the argument is the result of a shift-left
expression, there is some room for improvement here, and we can simply
use the bit count directly to calculate the value of T0SZ. At the same
time, we can omit calling GetRootTranslationTableInfo() to determine the
number of root table entries, and add a new helper that applies the
trivial calculation directly.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>