Shared glapi (libglapi.so) has been a requirement for years, in order
to build EGL.

Remove the no longer necessary dlopen/dlsym dance and link to the
library directly.

This allows us to remove a handful of platform specific workarounds, due
to the different name of the library.

v2:
 - Android: export the include dir (RobH)
 - Drop unused local variable (Eric)

Cc: Jonathan Gray <jsg@jsg.id.au>
Cc: Jon Turney <jon.turney@dronecode.org.uk>
Cc: Julien Isorce <julien.isorce@gmail.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com> (v1)
Tested-by: Tomasz Figa <tfiga@chromium.org> (v1)
Tested-by: Rob Herring <robh@kernel.org>