dispatch: GLES1 fixes for _mesa_create_exec_table().

dispatch: GLES1 fixes for _mesa_create_exec_table().

Currently, _mesa_create_exec_table() (in api_exec.c) is used for all
APIs except GLES1.  In GLES1, _mesa_create_exec_table_es1() (a code
generated function) is used instead.

In principle, this shouldn't be necessary.  It should be possible for
api_exec.c to contain the logic for populating the dispatch table for
all API's.

This patch paves the way for using _mesa_create_exec_table() instead
of _mesa_create_exec_table_es1(), by making _mesa_create_exec_table()
(and the functions it calls) expose the correct subset of desktop GL
functions for GLES1.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>