edid: Change HDR Static Metadata luminances to be float

They are float in libdisplay-info and our own EDID parsing also returns
a float but when then converted both to an integer. Especially the min
luminance can be <1.

We also don't need a variable for indicating presence of a CTA Static
Metadata block. The values are all zero if it is absent.

Found by Dor Askayo.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3574>

src/backends/edid.h

@@ -59,10 +59,9 @@ typedef enum
 
 struct _MetaEdidHdrStaticMetadata
 {
-  int available;
-  int max_luminance;
-  int min_luminance;
-  int max_fal;
+  float max_luminance;
+  float min_luminance;
+  float max_fal;
   MetaEdidTransferFunction tf;
   MetaEdidStaticMetadataType sm;
 };