lib/alloc_phys: Remove allocation accounting

The page allocator has better allocation tracking and is used by all
architectures, while the physical allocator is now never used for
allocating memory.

Simplify the physical allocator by removing allocation accounting. This
accomplishes two things:

1. It makes the allocator more useful, as the warning that was displayed
each allocation after the 256th is removed.

2. Together with the lock removal, the physical allocator becomes more
appealing as a very early allocator, when using the page allocator might
not be desirable or feasible.

Also, phys_alloc_show() has received a slight change in the way it displays
the use and free regions: the end of the region is now non-inclusive, to
allow phys_alloc_show() to express that no memory has been used, or no
memory is free, in which case the start and the end adresses are equal.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>