Ramdisk in the manifest, simplify initrd generation

We currently support loading a ramdisk for the primary. In fact, all
primaries are required to have one called 'initrd.img'. This makes
the ramdisk optional and specifies its filename in the manifest.

With that, generate_initrd.py loses the last remaining hardcoded
assumption about the structure of the Hafnium ramdisk. Refactor the
script and the build so that generate_initrd.py simply accepts a list of
(name in ramdisk, path on host) pairs.

Bug: 117551352
Change-Id: Iff2d70205940a1740c473d1cac34d5a05d6d6791
diff --git a/inc/hf/boot_flow.h b/inc/hf/boot_flow.h
index 3ecf25f..3307fb0 100644
--- a/inc/hf/boot_flow.h
+++ b/inc/hf/boot_flow.h
@@ -26,5 +26,6 @@
 		    struct mpool *ppool);
 
 bool boot_flow_update(struct mm_stage1_locked stage1_locked,
+		      const struct manifest *manifest,
 		      struct boot_params_update *p, struct memiter *cpio,
 		      struct mpool *ppool);