x86: Only enable EFI_CONSOLE if UART console is not enabled

Most x86 build configurations enable the UART console. Since EFI console
has also defaulted to enabled, this means that the EFI covers the early
part of the boot until UART takes over.

This is all fine, except that enabling EFI console has the effect of
disabling PRINTK_SYNC. This in turn has the effect of causing garbled
output over UART, which has led to several bug reports on x86 platforms
(in particular on up_squared).

Since EFI console should really only be used for early platform bringup
and debugging purposes, it's not really ideal to unconditionally have it
enabled by default. Instead, change the default enabling to be
conditional to the UART console being disabled.

Fixes #54861
Fixes #55071

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>