scheduling: Create a secondary sandbox scheduling domain

This updates the kernel configs to setup two domains instead of one,
and also defines a bare-bones domain scheduler that simply round-
robins through the domains.

Bug: 238811077
Change-Id: Ibb49f10265c38dc26235fc246f6147b306055bcb
GitOrigin-RevId: 6b17211d8866bec9207f78dc61c4840c6da9537d

kernel/round_robin_domain.c

@@ -0,0 +1,22 @@
+#include <model/statedata.h>
+#include <object/structures.h>
+
+/* Dual-domain schedule for Kata to isolate third party applications from system
+ * applications.
+ *
+ * Note that this doesn't actually implement the schedule -- that's hardwired in
+ * seL4's kernel source. See also kata/kernel/src/kernel/thread.c, in the
+ * nextDomain function around line 302 and the timerTick function around 630.
+ *
+ * Effectively this is a round-robin scheduler, so half of the CPU time is given
+ * to system applications, while third party applications are allocated the
+ * other half. Note that even if there's nothing to run in the third-party
+ * application domain, the scheduler will schedule an idle thread to ensure that
+ * domain gets it's allocated share of time.
+ */
+const dschedule_t ksDomSchedule[] = {
+    {.domain = 0, .length = 1},  // System domain
+    {.domain = 1, .length = 1},  // Third party application domain
+};
+
+const word_t ksDomScheduleLength = sizeof(ksDomSchedule) / sizeof(dschedule_t);