drm/sun4i: vi_scaler: Update DE33 base calculation

drm/sun4i: vi_scaler: Update DE33 base calculation

Now that channel base calculation is straightforward, let's update VI
scaler base calculation to be simpler. At the same time, also introduce
macro to avoid magic numbers.

Note, reason why current magic value and new macro value isn't the same
is because sun8i_channel_base() already introduces offset to channel
registers. Previous value is just the difference to VI scaler registers.
However, new code calculates scaler base from channel base. This is also
easier to understand when looking into BSP driver. Macro value can be
easily found whereas old diff value was not.

Reviewed-by: Chen-Yu Tsai <wens@kernel.org>
Tested-by: Ryan Walklin <ryan@testtoast.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://patch.msgid.link/20251104180942.61538-24-jernej.skrabec@gmail.com
Signed-off-by: Chen-Yu Tsai <wens@kernel.org>