accel: Rename accel_softmmu* -> accel_system*

Rename accel.softmmu -> accel.system in file paths
and the register_types() method.

Rename sysemu_stubs_ss -> system_stubs_ss in meson
following the pattern used on other source set names.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231004090629.37473-7-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/accel/meson.build b/accel/meson.build
index fda3157..5eaeb68 100644
--- a/accel/meson.build
+++ b/accel/meson.build
@@ -1,5 +1,5 @@
 specific_ss.add(files('accel-target.c'))
-system_ss.add(files('accel-softmmu.c', 'accel-blocker.c'))
+system_ss.add(files('accel-system.c', 'accel-blocker.c'))
 user_ss.add(files('accel-user.c'))
 
 subdir('tcg')