egl: move alloc & init out of _eglBuiltInDriver{DRI2,Haiku}

egl: move alloc & init out of _eglBuiltInDriver{DRI2,Haiku}

This is a revert of Marek's 84f3afc2e122cb418573 revert, with a missing
line added back. I failed a rebase and dropped that crucial line, and
didn't do a runtime test after my rebase, and as a result broke EGL for
everyone.
This commit has been tested by Intel's CI and I re-read it once more, so
it should be good this time.
--

Note: dropping the EGL_BAD_ALLOC in egl_haiku because it's
overwritten by the EGL_NOT_INITIALIZED in eglInitialize().

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>