anv: Add support for VK_KHR_draw_indirect_count

This implementation depends on the requirement for caller
to provide maxDrawCount which allows to issue maxDrawCount 3DPRIMITIVE
commands and have each of them predicate on
 draw_id < draw_count_from_buffer

'predicate_enable' flag will also be useful for VK_EXT_conditional_render

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>