drm/tests: Split drm_test_dp_mst_sideband_msg_req_decode into parameterized tests

The drm_test_dp_mst_sideband_msg_req_decode repeats the same test
structure with different parameters. This could be better represented
by parameterized tests, provided by KUnit.

In addition to the parameterization of the tests, the test case for the
client ID was changed: instead of using get_random_bytes to generate
the client ID, the client ID is now hardcoded in the test case. This
doesn't affect the assertively of the tests, as this test case only compare
the data going in with the data going out and it doesn't transform the data
itself in any way.

So, convert drm_test_dp_mst_sideband_msg_req_decode into parameterized
tests and make the tests' allocations and prints completely managed by KUnit.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20221001223422.857505-2-mcanal@igalia.com