gma: Introduce Generation type

It's the subset of `CPU_Type` that we have different compilation units
for. Also use it in the `Config` wherever we can decide something purely
on the `Generation` (i.e. don't mix `Gen` and `CPU` in expressions).

Change-Id: I5061021a80cd75ee3d7996ca343e6388b22bf341
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/27059
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/hw-gfx-gma-config_helpers.adb b/common/hw-gfx-gma-config_helpers.adb
index 57163a6..c95bebc 100644
--- a/common/hw-gfx-gma-config_helpers.adb
+++ b/common/hw-gfx-gma-config_helpers.adb
@@ -29,24 +29,23 @@
    is
    begin
       return
-        (case Config.CPU is
-            when G45 =>
+        (case Config.Gen is
+            when G45 =>                -- everything on GMCH
                (case Port is
                    when Internal     => LVDS,
                    when HDMI1 | DP1  => DIGI_B,
                    when HDMI2 | DP2  => DIGI_C,
                    when HDMI3 | DP3  => DIGI_D,
                    when Analog       => VGA),
-            when Ironlake .. Ivybridge => -- everything but eDP through FDI/PCH
+            when Ironlake =>           -- everything but eDP through FDI/PCH
               (if Config.Internal_Is_EDP and then Port = Internal then
                   DIGI_A
                else
-                 (case Pipe is
-                     -- FDIs are fixed to the CPU pipe
+                 (case Pipe is   -- FDIs are fixed to the CPU pipe
                      when Primary   => DIGI_B,
                      when Secondary => DIGI_C,
                      when Tertiary  => DIGI_D)),
-            when Haswell .. Skylake =>    -- everything but VGA directly on CPU
+            when others =>             -- everything but VGA directly on CPU
               (case Port is
                   when Internal     => DIGI_A,  -- LVDS not available
                   when HDMI1 | DP1  => DIGI_B,