ShellPkg: Shell package changes for RISC-V EDK2 CI.

ShellPkg: Shell package changes for RISC-V EDK2 CI.

Add RISC-V architecture to ShellPkg for EDK2 CI testing.

BZ:2562:
https://bugzilla.tianocore.org/show_bug.cgi?id=2562

Signed-off-by: Abner Chang <abner.chang@hpe.com>
Acked-by: Zhichao Gao <zhichao.gao@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Gilbert Chen <gilbert.chen@hpe.com>
Cc: Daniel Schaefer <daniel.schaefer@hpe.com>