target/arm: Implement gdbstub m-profile systemreg and secext

target/arm: Implement gdbstub m-profile systemreg and secext

The upstream gdb xml only implements {MSP,PSP}{,_NS,S}, but
go ahead and implement the other system registers as well.

Since there is significant overlap between the two, implement
them with common code.  The only exception is the systemreg
view of CONTROL, which merges the banked bits as per MRS.

Signed-off-by: David Reiss <dreiss@meta.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230227213329.793795-15-richard.henderson@linaro.org
[rth: Substatial rewrite using enumerator and shared code.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>