it's not that expensive but we call the endpoint that returns the boot
mode info very frequently, and EFI vars are provided by the firmware,
and there are lots of known cases where firmware was just a plain
mess.
So, don't risk that overly frequent reads will cause some weird side
effect and rather just cache the whole info, it cannot change without
a reboot anyway.
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>