BaseTools/Source/Python: Remove CPU architecture assumptions

BaseTools/Source/Python: Remove CPU architecture assumptions

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3308

The EDK II Build Specifications do not restrict the set of
CPU architectures that can be supported.  Remove places in
the EDK II that assume a fixed set of CPU architectures.

Remove build breaks in the following tools when a check against
a fixed set of CPU architectures is made.

* Build
* GenFds
* TargetTool

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Abner Chang <abner.chang@hpe.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>