centaurus/xorg: fix arch support

There's no std-def kernel on e2k and mipsel so far, and there are
different kernels for some aarch64 machines as well;  we'll have to
deal with this problem that's been solved in m-p-d the other way
around (@KFLAVOUR@ substitution in pkglists among the rest).

Also add graphics branding part: must be there regardless of platform,
otherwise an arbitrary one gets pulled in, this time it was
"xalt-kworkstation".  This is another case of the same problem,
m-p-d would solve it with @BRANDING@ substitution where m-p does
generation of variable contents but not file-based pkglists to
be put into the image for runtime selection during install process.

Restrict plymouth support to @X86 as well, just as bootsplash
branding component has already been.

pkg.in/lists/centaurus/xorg

@@ -42,23 +42,22 @@ x-cursor-theme-jimmac
 
 menu-icons-default
 
-branding-alt-server-graphics@X86
+branding-alt-server-graphics
 branding-alt-server-bootloader@X86
 branding-alt-server-bootsplash@X86
+make-initrd-plymouth@X86
 
 firefox-esr
 firefox-esr-ru
 firefox-esr-uk
 
-
 spice-vdagent
 xorg-drv-qxl
-kernel-modules-drm-std-def
-kernel-modules-drm-radeon-std-def
-kernel-modules-drm-nouveau-std-def
-kernel-modules-v4l-std-def
-kernel-modules-lirc-std-def
 
-make-initrd-plymouth
+kernel-modules-drm-std-def@!E2K
+kernel-modules-drm-radeon-std-def@!E2K
+kernel-modules-drm-nouveau-std-def@!E2K
+kernel-modules-v4l-std-def@!E2K
+kernel-modules-lirc-std-def@!E2K
+
 cpio
-branding-alt-server-bootsplash