Make autogen/simpasm work with RISCV-64 and PPC64LE cross compiler

[hanno-becker]

Within scripts/autogen, the update_via_simpasm routine detects the need for cross-compilation by comparing the target architecture to the native architecture. At the moment, we only detect x86 and AArch64, but the ongoing work on RISCV64 (#1037) and PPC64LE (#1184) backends will require support for those architectures as well. Further, scripts/cfify will need to be adjusted to accept those architectures.

Modify update_via_simpasm in scripts/autogen, as well as the --arch parameter in scripts/cfify, to allow for RISCV64 and PPC64LE sources.