xen: add missing MODULE_DESCRIPTION() macros

With ARCH=x86, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/xen/xen-pciback/xen-pciback.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/xen/xen-evtchn.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/xen/xen-privcmd.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20240611-md-drivers-xen-v1-1-1eb677364ca6@quicinc.comSigned-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/evtchn.c

@@ -729,4 +729,5 @@ static void __exit evtchn_cleanup(void)
 module_init(evtchn_init);
 module_exit(evtchn_cleanup);
 
+MODULE_DESCRIPTION("Xen /dev/xen/evtchn device driver");
 MODULE_LICENSE("GPL");

drivers/xen/privcmd-buf.c

@@ -19,6 +19,7 @@
 
 #include "privcmd.h"
 
+MODULE_DESCRIPTION("Xen Mmap of hypercall buffers");
 MODULE_LICENSE("GPL");
 
 struct privcmd_buf_private {

drivers/xen/privcmd.c

@@ -48,6 +48,7 @@
 
 #include "privcmd.h"
 
+MODULE_DESCRIPTION("Xen hypercall passthrough driver");
 MODULE_LICENSE("GPL");
 
 #define PRIV_VMA_LOCKED ((void *)1)

drivers/xen/xen-pciback/pci_stub.c

@@ -1708,5 +1708,6 @@ static void __exit xen_pcibk_cleanup(void)
 module_init(xen_pcibk_init);
 module_exit(xen_pcibk_cleanup);
 
+MODULE_DESCRIPTION("Xen PCI-device stub driver");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_ALIAS("xen-backend:pci");