cpu: Introduce CPUClass::gdb_{read,write}_register()

Completes migration of target-specific code to new target-*/gdbstub.c.

Acked-by: Michael Walle <michael@walle.cc> (for lm32)
Acked-by: Max Filippov <jcmvbkbc@gmail.com> (for xtensa)
Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/target-alpha/gdbstub.c b/target-alpha/gdbstub.c
index 1c18698..980f140 100644
--- a/target-alpha/gdbstub.c
+++ b/target-alpha/gdbstub.c
@@ -17,9 +17,14 @@
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */
+#include "config.h"
+#include "qemu-common.h"
+#include "exec/gdbstub.h"
 
-static int cpu_gdb_read_register(CPUAlphaState *env, uint8_t *mem_buf, int n)
+int alpha_cpu_gdb_read_register(CPUState *cs, uint8_t *mem_buf, int n)
 {
+    AlphaCPU *cpu = ALPHA_CPU(cs);
+    CPUAlphaState *env = &cpu->env;
     uint64_t val;
     CPU_DoubleU d;
 
@@ -52,8 +57,10 @@
     return gdb_get_regl(mem_buf, val);
 }
 
-static int cpu_gdb_write_register(CPUAlphaState *env, uint8_t *mem_buf, int n)
+int alpha_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
 {
+    AlphaCPU *cpu = ALPHA_CPU(cs);
+    CPUAlphaState *env = &cpu->env;
     target_ulong tmp = ldtul_p(mem_buf);
     CPU_DoubleU d;