SignedCapsulePkg: enable package build for AARCH64/ARM

SignedCapsulePkg: enable package build for AARCH64/ARM

This package is used by several platforms in edk2-platforms, so ensure it
can be built directly by adding AARCH64/ARM to SUPPORTED_ARCHITECTURES.

Also force-include CompilerIntrinsicsLib, BaseStackCheckLib and create a
resolution for ArmSoftFloatLib for ARM.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: jiewen.yao@intel.com