Improve debug output of the translation tables

The printed output has been improved in two ways:

- Whenever multiple invalid descriptors are found, only the first one
  is printed, and a line is added to inform about how many descriptors
  have been omitted.

- At the beginning of each line there is an indication of the table
  level the entry belongs to. Example of the new output:
  `[LV3] VA:0x1000 PA:0x1000 size:0x1000 MEM-RO-S-EXEC`

Change-Id: Ib6f1cd8dbd449452f09258f4108241eb11f8d445
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>