target/arm: Handle AArch64 gdb read/write regs in TYPE_ARM_CPU

target/arm: Handle AArch64 gdb read/write regs in TYPE_ARM_CPU

Instead of having the TYPE_AARCH64_CPU subclass set
CPUClass::gdb_read_register and ::gdb_write_register to different
methods from those of the TYPE_ARM_CPU parent class, have the
TYPE_ARM_CPU methods handle either AArch32 or AArch64 at runtime.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250317142819.900029-6-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>