exo: implement start of mariko fatal handler

exosphere/mariko_fatal/source/fatal_crt0.s

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+.section    .crt0.text.start, "ax", %progbits
+.align      6
+.global     _start
+_start:
+    /* Set the stack pointer to a temporary location. */
+    ldr x20, =0x1F00FC000
+    mov sp, x20
+
+    /* Initialize all memory to expected state. */
+    ldr x0, =__bss_start__
+    ldr x1, =__bss_end__
+    bl _ZN3ams6secmon5fatal10InitializeEmm
+
+    /* Jump to the fatal program. */
+    ldr x16, =_ZN3ams6secmon5fatal4MainEv
+    br x16