ext: hal: add openisa/vega_sdk_riscv

This provides a HAL for the OpenISA RV32M1 SoC.

Origin: open-isa-rv32m1 GitHub organization
URL: https://github.com/open-isa-rv32m1/rv32m1_sdk_riscv
Revision: 365b1060f0947d5250c07b3eebdbc9e54cd0246e
Maintained-by: External
License: BSD-3-Clause

Signed-off-by: Marti Bolivar <marti@foundries.io>