sysfb: Fix screen_info type check for VGA

Use the helper screen_info_video_type() to get the framebuffer
type from struct screen_info. Handle supported values in sorted
switch statement.

Reading orig_video_isVGA is unreliable. On most systems it is a
VIDEO_TYPE_ constant. On some systems with VGA it is simply set
to 1 to signal the presence of a VGA output. See vga_probe() for
an example. Retrieving the screen_info type with the helper
screen_info_video_type() detects these cases and returns the
appropriate VIDEO_TYPE_ constant. For VGA, sysfb creates a device
named "vga-framebuffer".

The sysfb code has been taken from vga16fb, where it likely didn't
work correctly either. With this bugfix applied, vga16fb loads for
compatible vga-framebuffer devices.

Fixes: 0db5b61e0dc0 ("fbdev/vga16fb: Create EGA/VGA devices in sysfb code")
Cc: Thomas Zimmermann <[e-mail]>
Cc: Javier Martinez Canillas <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Cc: Tzung-Bi Shih <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: "Uwe Kleine-König" <[e-mail]>
Cc: Zsolt Kajtar <[e-mail]>
Cc: <[e-mail]> # v6.1+
Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Tzung-Bi Shih <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/firmware/sysfb.c

···
 {
 	struct screen_info *si = &screen_info;
 	struct device *parent;
+	unsigned int type;
 	struct simplefb_platform_data mode;
 	const char *name;
 	bool compatible;
···
 			goto put_device;
 	}
 
+	type = screen_info_video_type(si);
+
 	/* if the FB is incompatible, create a legacy framebuffer device */
-	if (si->orig_video_isVGA == VIDEO_TYPE_EFI)
-		name = "efi-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_VLFB)
-		name = "vesa-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_VGAC)
-		name = "vga-framebuffer";
-	else if (si->orig_video_isVGA == VIDEO_TYPE_EGAC)
+	switch (type) {
+	case VIDEO_TYPE_EGAC:
 		name = "ega-framebuffer";
-	else
+		break;
+	case VIDEO_TYPE_VGAC:
+		name = "vga-framebuffer";
+		break;
+	case VIDEO_TYPE_VLFB:
+		name = "vesa-framebuffer";
+		break;
+	case VIDEO_TYPE_EFI:
+		name = "efi-framebuffer";
+		break;
+	default:
 		name = "platform-framebuffer";
+		break;
+	}
 
 	pd = platform_device_alloc(name, 0);
 	if (!pd) {