[prefix] Delay initrd image copy until memory map is ready

initrd_init() calls umalloc() to allocate space for the initrd image,
but does so before hide_etherboot() has been called.  It is therefore
possible for the initrd to end up overwriting iPXE itself.

Fix by converting initrd_init() from an init_fn to a startup_fn.

Originally-fixed-by: Till Straumann <strauman@slac.stanford.edu>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/core/runtime.c

 	DBGC ( colour, "RUNTIME found command line \"%s\" at %08x\n",
 	       cmdline, cmdline_phys );
 
+	/* Mark command line as consumed */
+	cmdline_phys = 0;
+
 	/* Strip unwanted cruft from the command line */
 	cmdline_strip ( cmdline, "BOOT_IMAGE=" );
 	cmdline_strip ( cmdline, "initrd=" );
 	memcpy_user ( image->data, 0, phys_to_user ( initrd_phys ), 0,
 		      initrd_len );
 
+	/* Mark initrd as consumed */
+	initrd_phys = 0;
+
 	/* Register image */
 	if ( ( rc = register_image ( image ) ) != 0 ) {
 		DBGC ( colour, "RUNTIME could not register initrd: %s\n",
 }
 
 /** Command line and initrd initialisation function */
-struct init_fn runtime_init_fn __init_fn ( INIT_NORMAL ) = {
-	.initialise = runtime_init,
+struct startup_fn runtime_startup_fn __startup_fn ( STARTUP_NORMAL ) = {
+	.startup = runtime_init,
 };