exo: add sdmmc test program

exosphere/sdmmc_test/source/sdmmc_test_start.s

@@ -0,0 +1,37 @@
+/*
+ * 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._ZN3ams10sdmmc_test5StartEv, "ax", %progbits
+.align      3
+.global     _ZN3ams10sdmmc_test5StartEv
+_ZN3ams10sdmmc_test5StartEv:
+    /* Switch to system mode, mask all interrupts, clear all flags */
+    msr cpsr_cxsf, #0xDF
+
+    /* Set the stack pointer. */
+    ldr sp, =__stack_top__
+
+    /* Set our link register to the exception handler. */
+    ldr lr, =_ZN3ams10sdmmc_test16ExceptionHandlerEv
+
+    /* Call init array functions. */
+    bl __libc_init_array
+
+    /* Invoke main. */
+    b _ZN3ams10sdmmc_test4MainEv
+
+    /* Infinite loop. */
+    2: b 2b