Add support to formats %i, %d, %p, %x and %u for left-padding numbers
with zeroes (e.g. `%08x`).

Change-Id: Ifd4795a82a8d83da2c00b44b9e482a2d9be797e3
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>