[lkrnprefix] Support a longer version string

The bzImage specification allows two bytes for the setup code jump
instruction at offset 0x200, which limits its relative offset to +0x7f
bytes.  This currently imposes an upper limit on the length of the
version string, which currently precedes the setup code.

Fix by moving the version string to the .prefix.data section, so that
it no longer affects the placement of the setup code.

Originally-fixed-by: Miao Wang <shankerwangmiao@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Author: mcb30

src/arch/x86/prefix/lkrnprefix.S

@@ -104,6 +104,7 @@ hardware_subarch:
 hardware_subarch_data:
 	.byte	0, 0, 0, 0, 0, 0, 0, 0
 
+	.section ".prefix.data", "aw", @progbits
 version_string:
 	.asciz	VERSION
 
@@ -113,6 +114,7 @@ version_string:
  *
  */
 
+	.section ".prefix", "ax", @progbits
 setup:
 	/* Fix up code segment */
 	pushw	%ds