drm/ssd130x: Add per-family update backlight logic

ssd130x_update_bl() runs for every SSD13xx panel, but it only works for
SSD130x and SSD132x: it writes the single global SSD13XX_CONTRAST (0x81)
command, which those two families expose.  SSD133x has no such command --
it has three per-channel contrast registers (CONTRAST_A/B/C) that must be
scaled together -- so ssd130x_update_bl() has no effect on it.

Make backlight_ops.update_status a per-family choice.  SSD130x and SSD132x
keep ssd130x_update_bl() because they share the SSD13XX_CONTRAST interface,
while SSD133x gets ssd133x_update_bl(), which drives the three channels
through ssd133x_set_contrast().

Signed-off-by: Amit Barzilai <amit.barzilai22@gmail.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patch.msgid.link/20260729053054.29374-3-amit.barzilai22@gmail.com
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>

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