lowlevel-blt-bench: add test name parser and self-test

lowlevel-blt-bench: add test name parser and self-test

This patch is inspired by "lowlevel-blt-bench: Parse test name strings in
general case" by Ben Avison. From Ben's commit message:

"There are many types of composite operation that are useful to benchmark
but which are omitted from the table. Continually having to add extra
entries to the table is a nuisance and is prone to human error, so this
patch adds the ability to break down unknow strings of the format
  <operation>_<src>[_<mask]_<dst>[_ca]
where bitmap formats are specified by number of bits of each component
(assumed in ARGB order) or 'n' to indicate a solid source or mask."

Add the parser to lowlevel-blt-bench.c, but do not hook it up to the
command line just yet. Instead, make it run a self-test.

As we now dynamically parse strings similar to the test names in the
huge table 'tests_tbl', we should make sure we can parse the old
well-known test names and produce exactly the same test parameters. The
self-test goes through this old table and verifies the parsing results.

Unfortunately the old table is not exactly consistent, it contains some
special cases that cannot be produced by the parsing rules. Whether
these special cases are intentional or just an oversight is not always
clear. Anyway, add a small table to reproduce the special cases
verbatim.

If we wanted, we could remove the big old table in a follow-up commit,
but then we would also lose the parser self-test.

The point of this whole excercise to let lowlevel-blt-bench recognize
novel test patterns in the future, following exactly the conventions
used in the old table.

Ben, from what I see, this parser has one major difference to what you
wrote. For a solid mask, your parser uses a8r8g8b8 format, while mine
uses a8 which comes from the old table.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Ben Avison <bavison@riscosopen.org>