plugins: Introduce PLUGIN_CB_MEM_REGULAR

Use different enumerators for vcpu_udata and vcpu_mem callbacks.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/qemu/plugin.h

@@ -68,6 +68,7 @@ union qemu_plugin_cb_sig {
 
 enum plugin_dyn_cb_type {
     PLUGIN_CB_REGULAR,
+    PLUGIN_CB_MEM_REGULAR,
     PLUGIN_CB_INLINE,
 };