ArmPlatformPkg: change PcdBdsLinuxSupport default value

ArmPlatformPkg: change PcdBdsLinuxSupport default value

The built-in Linux Loader is obsolete and not included in most builds.
The patch sets the PcdBdsLinuxSupport default value to FALSE and prevents
ArmBds from looking for built-in Linux Loader by default and ASSERTing
when it cannot be found. Platforms which still using built-in loader have
to set this PCD in their platform description file.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Daniil Egranov <daniil.egranov@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>