egl: Fix creation of compatibility contexts

wegl_context_create() ignored wcore_config_attrs::context_profile and
never set EGL_CONTEXT_OPENGL_PROFILE_MASK_KHR. The default value of
EGL_CONTEXT_OPENGL_PROFILE_MASK_KHR is
EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT_KHR. Therefore, for context versions
>= 3.2,  wegl_context_create() always created a core context.

This patch fixes wegl_context_create() to inspect
wcore_config_attrs::context_profile and set
EGL_CONTEXT_OPENGL_PROFILE_MASK_KHR accordingly.

(Whoo! Waffle has an issue tracker now, and the 'Fixes' tag below will
automatically close the issue when patch hits master!)

Fixes: https://github.com/waffle-gl/waffle/issues/1
Reported-by: Jordan Justen <jordan.l.justen@intel.com> @jljusten
Signed-off-by: Chad Versace <chad.versace@linux.intel.com> @chadversary