drm/rockchip: dw_hdmi: switch to FIELD_PREP_WM16* macros

The era of hand-rolled HIWORD_UPDATE macros is over, at least for those
drivers that use constant masks.

Remove this driver's very own HIWORD_UPDATE macro, and replace all
instances of it with equivalent instantiations of FIELD_PREP_WM16 or
FIELD_PREP_WM16_CONST, depending on whether it's in an initializer.

This gives us better error checking, and a centrally agreed upon
signature for this macro, to ease in code comprehension.

Because FIELD_PREP_WM16/FIELD_PREP_WM16_CONST shifts the value to the
mask (like FIELD_PREP et al do), a lot of macro instantiations get
easier to read.

This was tested on an RK3568 ODROID M1, as well as an RK3399 ROCKPro64.

Reviewed-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Tested-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>