syslinux.bbclass, syslinux: Update to syslinux 6.01

syslinux.bbclass, syslinux: Update to syslinux 6.01

A newer version of syslinux is required for an EFI enabled isohybrid.
This is used for the the capability to generate 3 types of ISO images,
all of which can be booted off a USB device or HDD if copied with dd.

1) PC BIOS only ISO
2) EFI only ISO
3) EFI + PC BIOS ISO

The syslinux.bbclass required a minor tweak because a few .c32
libraries require dynamic loading from the created media as of
syslinux 5 and up.  This was a good time to also fix the
duplication of the AUTO_SYSLINUXMENU block.

[YOCTO #4100]

(From OE-Core rev: 17d74fbd09e377e100423e1a73b9d4ce761a21d7)

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>