wegl: fix wegl_util.h includes and declarations
wegl: fix wegl_util.h includes and declarations

Remove unnecessary includes.
Add needed forward struct declarations.

Signed-off-by: Frank Henigman <4f3ccfa167f952ff7263448ff4377acff6a23e5c@google.com>
Reviewed-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@intel.com>

waffle-gl/waffle,fjhenigman/waffle,waffle-gl/waffle,waffle-gl/waffle,evelikov/waffle,evelikov/waffle,dcbaker/waffle,dcbaker/waffle,fjhenigman/waffle,evelikov/waffle,chadversary/waffle,waffle-gl/waffle,chadversary/waffle,fjhenigman/waffle,dcbaker/waffle,chadversary/waffle