vboot: Add flag to vbutil_kernel for reconstruction of vmlinuz image

Adding functionality to allow for rebuilding of vmlinuz after it
has been processed into vblock and header stripped.  Basically appends
the 16-bit header of a vmlinuz image onto the end of the vblock.
BUG=chromium:438302
BRANCH=none
TEST=Successfully ran "make runalltests".
     Also, ran:
     1. Repack kernel block (so that 16-bit header is included):
        "vbutil_kernel --pack kern_0 ..."
     2. Verify kernel: "vbutil_kernel --verify kern_0 ... ".  This should
        be done before booting into kernel, but not necessary for it to work.
     3. Rebuild vmlinuz image:
        "vbutil_kernel --get-vmlinuz kern_0 --vmlinuz-out vm.out"
     4. Set up kexec with vmlinuz (this should complete with no errors):
        "kexec -l vm.out (other kernel cmd line args)"
     5. Boot into kernel:
        "kexec -e"

Change-Id: Iaa1582a1aedf70b43cdb3a56cde1fb248f1793d4
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/232750
Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>

host/lib/include/host_common.h

@@ -50,6 +50,8 @@ VbKernelPreambleHeader *CreateKernelPreamble(
 	uint64_t bootloader_address,
 	uint64_t bootloader_size,
 	const VbSignature *body_signature,
+	uint64_t vmlinuz_header_address,
+	uint64_t vmlinuz_header_size,
 	uint64_t desired_size,
 	const VbPrivateKey *signing_key);