When working out which initrds to regenerate, it is likely that the
same initrd symlink is used by multiple bootloader entries (i.e.
typically the initrd.img symlinked initrd is used by both the current
and the failsafe entry).
If the earlier entry does have vga= but the latter entry does not,
then the latter entry will end up being the value used when
checking the vga= argument when deciding if the initrd
needs to be regenerated.
Thus we only expand the symlink if the vga= value is set
which means that any initrd that needs to be regenerated
definitely will be regenerated.
This will hopefully solve the problem seen on mga2 when
and updated theme package had to be pushed but the initrds
didn't seem to be updated.