New processor language variant needed for SIlicon Labs CIP-51 (C8051Fxxx) family

[gtackett]

Is your feature request related to a problem? Please describe.
In order to add support to Ghidra for the Silicon Labs CIP-51 (originally created by Cygnal Integrated Products, which was later acquired by Silicon Labs), 8051.ldefs needs a new variant of the 8051 processor.

The need for a new variant is driven by features of the CIP-51 and supporting compilers that can't be adequately handled with any of the existing variants. The solution description below discusses some of these.

Describe the solution you'd like

CIP-51 implements the basic 8051 instruction set as the original 8051, adding a small number of CIP51-specific instructions.

Its memory model is also based on the original 8051, but with extensions to allow for additional memory and peripheral devices.

There are at least two compilers/toolchains that specifically support CIP-51 extensions to the 8051:

• ARM Keil's C51/CX51
• IAR Embedded Workbench

Describe alternatives you've considered
Extensions to the 8051 as implemented in existing variants--mx51, 80251, 80390, and mx51--can't be used to accurately and adequately describe the extensions present in CIP-51.

Additional context
I intend to offer proposed changes to 8051.ldefs via the usual github code change cycle. Improvements to whatever I may offer will of course be encouraged!

To fully achieve support for CIP51, changes to other files in languages will of course be necessary. If/when I understand what's needed, I'll submit additional new feature requests.