powerpc/boot: Update Makefile comment for 64bit wrapper

As of commit 147c0516 ("powerpc/boot: Add support for 64bit little
endian wrapper") the comment in the Makefile is misleading. The wrapper
packaging 64bit kernel may built as a 32 or 64 bit elf. Update the
comment to reflect this.
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200825035147.3239-1-jniethe5@gmail.com

arch/powerpc/boot/Makefile

@@ -7,7 +7,7 @@
 # Based on coffboot by Paul Mackerras
 # Simplified for ppc64 by Todd Inglett
 #
-# NOTE:	this code is built for 32 bit in ELF32 format even though
+# NOTE:	this code may be built for 32 bit in ELF32 format even though
 #	it packages a 64 bit kernel.  We do this to simplify the
 #	bootloader and increase compatibility with OpenFirmware.
 #