mesa/main: fix validation of GL_TIME_ELAPSED

mesa/main: fix validation of GL_TIME_ELAPSED

ctx->Extensions.EXT_timer_query is set based on the driver-
capabilities, not based on the context type. We need to check against
_mesa_has_EXT_timer_query(ctx) instead to figure out if the extension
is really supported. We also need to check for
EXT_disjoint_timer_query, which enables the same functionality for ES.

This turns usage of GL_TIME_ELAPSED into an error on ES 3, as is
required by the spec.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>