loader: VESA: make nvidia scaling fixup a driver setting

Since not everyone likes the default, make it an option in the vesa
settings file. Note setting a mode with the Screen prefs overwrites
the file so it will discard the option.

Also move the code to get_mode_from_settings() since we can't load driver
settings as early as vesa_init().

Change-Id: I93080bd1fbc064dab053624ad37935268b1ed17d

data/settings/kernel/drivers/vesa

@@ -2,3 +2,8 @@
 # mode {x-resolution} {y-resolution} {bitdepth},
 #   for example:
 #mode 1280 1024 32
+
+# Set NVIDIA scaling mode
+# 1: disable scaling completely
+# other modes are available depending on the BIOS
+#nvidia_scaling 1