drm/arm/hdlcd: Replace struct simplefb_format with custom type

Map DRM FourCC codes to pixel descriptions with an internal struct
type. Avoid simplefb's struct simplefb_format, which is for parsing
"simple-framebuffer" DT nodes. Drop the unsupported formats with
alpha channel from the list.

The HDLCD drivers uses struct simplefb_format and its default
initializer SIMPLEFB_FORMATS to map DRM_FORMAT_ constants to pixel
descriptions. The simplefb helpers are for parsing "simple-framebuffer"
DT nodes and should be avoided in other context. Therefore replace it
in hdlcd with a custom struct type and pixel descriptions from
PIXEL_FORMAT_ constants.

This change also removes including <linux/platform_data/simplefb.h>,
which includes several unrelated headers, such as <linux/fb.h>.

v2:
- drop unsupported alpha formats (Liviu)
- keep original sorting of formats (Javier)
- use anonymous type for supported_formats

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://lore.kernel.org/r/20250610073027.322944-1-tzimmermann@suse.de