target/arm: gdbstub: Guard M-profile code with CONFIG_TCG

target/arm: gdbstub: Guard M-profile code with CONFIG_TCG

This code is only relevant when TCG is present in the build. Building
with --disable-tcg --enable-xen on an x86 host we get:

$ ../configure --target-list=x86_64-softmmu,aarch64-softmmu --disable-tcg --enable-xen
$ make -j$(nproc)
...
libqemu-aarch64-softmmu.fa.p/target_arm_gdbstub.c.o: in function `m_sysreg_ptr':
 ../target/arm/gdbstub.c:358: undefined reference to `arm_v7m_get_sp_ptr'
 ../target/arm/gdbstub.c:361: undefined reference to `arm_v7m_get_sp_ptr'

libqemu-aarch64-softmmu.fa.p/target_arm_gdbstub.c.o: in function `arm_gdb_get_m_systemreg':
../target/arm/gdbstub.c:405: undefined reference to `arm_v7m_mrs_control'

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Message-id: 20230628164821.16771-1-farosas@suse.de
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>