syslinux.bbclass: Backport newer version from oe-core

:Release Notes:
We need newer version in order to fix text console in vmdk images
for emulator.

:Detailed Notes:
Tracked by upstream report:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=3944

:Testing Performed:

:QA Notes:

:Issues Addressed:
[YOCTO-3944] syslinux.bbclass needs some work to add serial support
             and a real menu
[GF-7485]    emulator is writing boot messages to screen

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I904a6e4065f8b3d2018666b04cb8e4eaa3cb392e
Reviewed-on: https://g2g.palm.com/3384
Reviewed-by: Build Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>