cbfs: Introduce cbfs_ro_map() and cbfs_ro_load()

This patch introduces two new CBFS API functions which are equivalent to
cbfs_map() and cbfs_load(), respectively, with the difference that they
always operate on the read-only CBFS region ("COREBOOT" FMAP section).
Use it to replace some of the simple cases that needed to use
cbfs_locate_file_in_region().

Change-Id: I9c55b022b6502a333a9805ab0e4891dd7b97ef7f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39306
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/quark/romstage/romstage.c

@@ -49,29 +49,16 @@ void disable_rom_shadow(void)
 
 void *locate_rmu_file(size_t *rmu_file_len)
 {
-	struct cbfsf fh;
 	size_t fsize;
 	void *rmu_data;
-	uint32_t type;
 
 	/* Locate the rmu.bin file in the read-only region of the flash */
-	type = CBFS_TYPE_RAW;
-	if (cbfs_locate_file_in_region(&fh, "COREBOOT", "rmu.bin", &type))
+	rmu_data = cbfs_ro_map("rmu.bin", &fsize);
+	if (!rmu_data)
 		return NULL;
 
-	/* Get the file size */
-	fsize = region_device_sz(&fh.data);
 	if (rmu_file_len != NULL)
 		*rmu_file_len = fsize;
 
-	/* Get the data address */
-	rmu_data = rdev_mmap(&fh.data, 0, fsize);
-
-	/* Since the SPI flash is directly mapped into memory, we do not need
-	 * the mapping provided by the rdev service.  Unmap the file to prevent
-	 * a memory leak.  Return/leak the SPI flash address for the rmu.bin
-	 * file data which will be directly accessed by FSP MemoryInit.
-	 */
-	rdev_munmap(&fh.data, rmu_data);
 	return rmu_data;
 }