sd fs: Move sd init/mount/helpers to their own object

bootloader/hos/hos_config.c

@@ -22,6 +22,7 @@
 #include "fss.h"
 #include "../libs/fatfs/ff.h"
 #include "../mem/heap.h"
+#include "../storage/nx_sd.h"
 #include "../utils/dirlist.h"
 
 #include "../gfx/gfx.h"
@@ -29,8 +30,6 @@
 //#define DPRINTF(...) gfx_printf(__VA_ARGS__)
 #define DPRINTF(...)
 
-extern void *sd_file_read(const char *path, u32 *fsize);
-
 static int _config_warmboot(launch_ctxt_t *ctxt, const char *value)
 {
 	ctxt->warmboot = sd_file_read(value, &ctxt->warmboot_size);