lib/vsprintf: Add support for architectural capabilities

Introduce new printk's pointer format extension to support capabilities,
with one being denoted by specifying the 'l' length modifier alongside
the 'p' type character => "%lp". In addition to the raw capability
format, adding '#' flag will generate the simplified one, being slightly
more verbose. In both cases, the actual result is subject to
pointer hashing (address only) unless either 'x' qualifier or
no_hash_pointers command line parameter is being provided.
For more details see the docs, updated here as well.

While at it, add some testcases to validate new format alongside
checkpatchpl new warning, to raise the awareness of potential misuse.

Signed-off-by: Beata Michalska <beata.michalska@arm.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>