x86/shim: use credit scheduler

Remove sched=null from shim cmdline and doc

We use the default scheduler (credit1 as of writing). The NULL
scheduler still has bugs to fix.

Update shim.config.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
(cherry picked from commit 831cbe98f6)

docs/man/xl.cfg.pod.5.in

@@ -531,7 +531,7 @@ Ignored if pvhsim is false.
 =item B<pvshim_cmdline="STRING">
 
 Command line for the shim.
-Default is "pv-shim console=xen,pv sched=null".
+Default is "pv-shim console=xen,pv".
 Ignored if pvhsim is false.
 
 =item B<pvshim_extra="STRING">

tools/libxl/libxl_internal.h

@@ -119,7 +119,7 @@
 #define DOMID_XS_PATH "domid"
 #define INVALID_DOMID ~0
 #define PVSHIM_BASENAME "xen-shim"
-#define PVSHIM_CMDLINE "pv-shim console=xen,pv sched=null"
+#define PVSHIM_CMDLINE "pv-shim console=xen,pv"
 
 /* Size macros. */
 #define __AC(X,Y)   (X##Y)