package/libepoxy: bump to version 1.5.4

This release contains two minor improvements (smaller library size, and
updates to the GL registry), plus a couple of build fixes which are not
relevant for Buildroot (one for Solaris; another for unit tests, which
we do not build):

  https://github.com/anholt/libepoxy/releases/tag/1.5.4



Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>