platform/x86: think-lmi: Split current_value to reflect only the value

Currently attributes will show things like:
`BootOrderLock,Disable`
rather than just
`Disable`.

Of course this works, but the attribute is intended to be read by
userspace tools and not require further processing.  That is a userspace
tool can display a drop down of `possible_values` and `current_value` is
one of them from the list.

This also aligns `think-lmi` with how `dell-wmi-sysman` works.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://lore.kernel.org/r/20210622200755.12379-3-mario.limonciello@amd.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>