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

This patch add new macros which are used to set the following
registers:
- VIU_SW_RESET
- VIU_OSD1_CTRL_STAT
- VIU_OSD2_CTRL_STAT
- VIU_OSD1_FIFO_CTRL_STAT
- VIU_OSD2_FIFO_CTRL_STAT
- VIU_MISC_CTRL0
- VIU_OSD_BLEND_CTRL
- OSD1_BLEND_SRC_CTRL
- OSD2_BLEND_SRC_CTRL
- DOLBY_PATH_CTRL

Signed-off-by: Julien Masson <jmasson@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
[narmstrong: fix OSD1_BLEND_SRC_CTRL register init value for G12A]
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/86sgrz82em.fsf@baylibre.com