dracut: add few more setting to reduce initramfs size on Debian

Review content of initramfs on Debian, and remove biggest yet unused
parts.

QubesOS/qubes-issues#8649

boot/dracut-qubes.conf

@@ -14,3 +14,10 @@ omit_dracutmodules+=" ifcfg qemu-net i18n resume mdraid terminfo crypt lunmask n
 # confidential computing is not a Qubes feature). This saves about 5MB (20%) of
 # initramfs size.
 omit_dracutmodules+=" tpm2-tss "
+
+# Exclude plymouth, as it pulls in a lot of graphical stack, including GPU
+# drivers, and none of the boot screen is visible in a qube anyway
+omit_dracutmodules+=" plymouth "
+
+# Exclude microcode, as VM cannot load it anyway, saves over 10MB of space
+early_microcode="no"