EmbeddedPkg: add driver to set graphical/serial console preference

EmbeddedPkg: add driver to set graphical/serial console preference

Linux on ARM/arm64 will infer from the presence of a /chosen/stdout-path
DT property or of a SPCR ACPI table that the primary console is the serial
port, even if a graphical console is available as well.

So let's introduce a driver that allows the user to set a preference
between graphical and serial if both are available. If the preference
is set to 'Graphical', and any GOP protocol instances have been installed
by the time the ReadyToBoot event is signalled, remove the DT property
and/or the SPCR table entirely.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>