boot/syslinux: fix build with glibc 2.28+

When building with glibc 2.28+, the "major", "minor" and "makedev"
functions are defined in "sys/sysmacros.h". This commit backports
upstream commit 1a74985b2a404639b08882c57f3147229605dfd5 to fix the
build with glibc 2.28.

Link: https://www.syslinux.org/wiki/index.php?title=Building


Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>