xen/tmem: Remove the usage of 'noselfshrink' and use 'tmem.selfshrink' bool instead.

As the 'tmem' driver is the one that actually sets whether
it will use it or not so might as well make tmem responsible
for this knob.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index f03bf50..98e9744 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -22,7 +22,7 @@
 	  ballooning is disabled by default but can be enabled with the
 	  'selfballooning' kernel boot parameter.  If FRONTSWAP is configured,
 	  frontswap-selfshrinking is enabled by default but can be disabled
-	  with the 'noselfshrink' kernel boot parameter; and self-ballooning
+	  with the 'tmem.selfshrink=0' kernel boot parameter; and self-ballooning
 	  is enabled by default but can be disabled with the 'noselfballooning'
 	  kernel boot parameter.  Note that systems without a sufficiently
 	  large swap device should not enable self-ballooning.