Add some basic fat32 code

sw/kernel/filesystems/fat32.h

@@ -0,0 +1,34 @@
+#ifndef _FAT32_H
+#define _FAT32_H
+
+#include <stdint.h>
+
+void fat32_init();
+
+struct fat32_directory_entry {
+    char file_name[8];
+    char file_ext[3];
+    uint8_t attr1;
+    uint8_t create_time_10ms;
+    uint16_t create_time;
+    uint16_t create_date;
+    uint16_t access_date;
+    uint16_t cluster_high;
+    uint16_t modified_time;
+    uint16_t modified_date;
+    uint16_t cluster_low;
+    uint32_t file_size;
+};
+
+struct lfn_entry {
+    uint8_t sequence_number;
+    uint16_t name_0[5];
+    uint8_t attributes;
+    uint8_t type;
+    uint8_t checksum;
+    uint16_t name_1[6];
+    uint16_t cluster_low;
+    uint16_t name_2[2];
+};
+
+#endif