lib: os: disable PRINTK_SYNC while using EFI console as log backend

There is a spinlock used in the EFI console code for printing
one line string. It already made the log output being in order
under multi-cores, so it doesn't need a printk sync spinlock
again. Disable it while using EFI console as a log backend.

Fixes #47512.

Signed-off-by: Enjia Mai <enjia.mai@intel.com>