[RISCV] Add Syntacore SCR1 CPU model
SCR1 is available at https://github.com/syntacore/scr1
'scr1-base' corresponds to SCR1_CFG_RV32IC_BASE,
'scr1-max' corresponds to SCR1_CFG_RV32IMC_MAX.
SCR1_CFG_RV32EC_MIN is RV32EC, which is currently unsupported.
Alphabetise (with the exception of INVALID)?