MdeModulePkg/EbcDxe AARCH64: simplify interpreter entry point thunks

MdeModulePkg/EbcDxe AARCH64: simplify interpreter entry point thunks

The prototypes of EbcInterpret() and ExecuteEbcImageEntryPoint() are
private to the AARCH64 implementation of EbcDxe, so we can shuffle
the arguments around a bit and make the assembler thunking glue a lot
simpler.

For ExecuteEbcImageEntryPoint(), this involves passing the EntryPoint
argument as the third parameter, rather than the first, which allows
us to do a tail call. For EbcInterpret(), instead of copying each
argument beyond #8 from one native stack frame to the next (before
another copy is made into the VM stack), pass a pointer to the
argument stack.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Feng Tian <feng.tian@intel.com>