drm/vc4: vec: Fix definition of PAL-M mode

PAL-M is a Brazilian analog TV standard that uses a PAL-style chroma
subcarrier at 3.575611[888111] MHz on top of 525-line (480i60) timings.
This commit makes the driver actually use the proper VEC preset for this
mode instead of just changing PAL subcarrier frequency.

Acked-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v4-25-60d38873f782@cerno.tech


Signed-off-by: Maxime Ripard <maxime@cerno.tech>