drm: meson: vpp: use proper macros instead of magic constants

This patch add new macros which are used to set the following
registers:
- VPP_OSD_SCALE_COEF_IDX
- VPP_DOLBY_CTRL
- VPP_OFIFO_SIZE
- VPP_HOLD_LINES
- VPP_SC_MISC
- VPP_VADJ_CTRL

Signed-off-by: Julien Masson <jmasson@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
[narmstrong: put back 0x1020080 in VPP_DUMMY_DATA1 for GXM]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/86tvcf82eu.fsf@baylibre.com