test: Move some SPL-loading test-code into sandbox common

This code is useful for loading an image in sandbox_spl so move it into
a place where it can be called as needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/image/spl_load_os.c b/test/image/spl_load_os.c
index 7d5fb9b..56105a5 100644
--- a/test/image/spl_load_os.c
+++ b/test/image/spl_load_os.c
@@ -10,63 +10,12 @@
 #include <test/spl.h>
 #include <test/ut.h>
 
-/* Context used for this test */
-struct text_ctx {
-	int fd;
-};
-
-static ulong read_fit_image(struct spl_load_info *load, ulong offset,
-			    ulong size, void *buf)
-{
-	struct text_ctx *text_ctx = load->priv;
-	off_t ret;
-	ssize_t res;
-
-	ret = os_lseek(text_ctx->fd, offset, OS_SEEK_SET);
-	if (ret != offset) {
-		printf("Failed to seek to %zx, got %zx (errno=%d)\n", offset,
-		       ret, errno);
-		return 0;
-	}
-
-	res = os_read(text_ctx->fd, buf, size);
-	if (res == -1) {
-		printf("Failed to read %lx bytes, got %ld (errno=%d)\n",
-		       size, res, errno);
-		return 0;
-	}
-
-	return size;
-}
-
 static int spl_test_load(struct unit_test_state *uts)
 {
 	struct spl_image_info image;
-	struct legacy_img_hdr *header;
-	struct text_ctx text_ctx;
-	struct spl_load_info load;
 	char fname[256];
-	int ret;
-	int fd;
 
-	memset(&load, '\0', sizeof(load));
-	spl_set_bl_len(&load, 512);
-	load.read = read_fit_image;
-
-	ret = sandbox_find_next_phase(fname, sizeof(fname), true);
-	if (ret)
-		ut_assertf(0, "%s not found, error %d\n", fname, ret);
-
-	header = spl_get_load_buffer(-sizeof(*header), sizeof(*header));
-
-	fd = os_open(fname, OS_O_RDONLY);
-	ut_assert(fd >= 0);
-	ut_asserteq(512, os_read(fd, header, 512));
-	text_ctx.fd = fd;
-
-	load.priv = &text_ctx;
-
-	ut_assertok(spl_load_simple_fit(&image, &load, 0, header));
+	ut_assertok(sandbox_spl_load_fit(fname, sizeof(fname), &image));
 
 	return 0;
 }