Reading/Writing registers from RV32E ISA targets uses incorrect register count

[perigoso]

RV32E base ISA devices have 16 GPRs while RV32I base ISA devices have 32, this is correctly reported to gdb in the target description xml, but when reading or writing all registers BMD still considers 32 registers to be present.

The main symptom is GDB reporting incorrect length for 'g' packets:
Remote 'g' packet reply is too long (expected 104 bytes, got 132 bytes): ....

[perigoso]

A fix commit (d1b2b5a) is present in #1399