xlat lib v2: Print some debug statistics

xlat lib v2: Print some debug statistics

This patch adds some debug prints to display some statistics about page
tables usage. They are printed only if the LOG_LEVEL is at least 50
(i.e. VERBOSE).

Sample output for BL1:

VERBOSE:    Translation tables state:
VERBOSE:      Max allowed PA:  0xffffffff
VERBOSE:      Max allowed VA:  0xffffffff
VERBOSE:      Max mapped PA:   0x7fffffff
VERBOSE:      Max mapped VA:   0x7fffffff
VERBOSE:      Initial lookup level: 1
VERBOSE:      Entries @initial lookup level: 4
VERBOSE:      Used 4 sub-tables out of 5 (spare: 1)

Change-Id: If38956902e9616cdcd6065ecd140fe21482597ea
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>