intel/assembler: Add labels support

Use labels instead of numeric JIP/UIP offsets.
Works for gen6+.

v2:
 - Change asm tests to use labels on gen6+
 - Remove usage of relative offsets on gen6+
 - Consider brw_jump_scale when setting relative offset
 - Return error if there is a JIP/UIP label without matching target
 - Fix matching of label tokens

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4245>