target/arm: Use GDBFeature for dynamic XML

target/arm: Use GDBFeature for dynamic XML

In preparation for a change to use GDBFeature as a parameter of
gdb_register_coprocessor(), convert the internal representation of
dynamic feature from plain XML to GDBFeature.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20231213-gdb-v17-1-777047380591@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240227144335.1196131-6-alex.bennee@linaro.org>