i965/eu: Refactor jump distance scaling to use a helper function.

i965/eu: Refactor jump distance scaling to use a helper function.

Different generations of hardware measure jump distances in different
units.  Previously, every function that needed to set a jump target open
coded this scaling, or made a hardcoded assumption (i.e. just used 2).

Most functions start with the number of instructions to jump, and scale
up to the hardware-specific value.  So, I made the function match that.

Others start with a byte offset, and divide by a constant (8) to obtain
the jump distance.  This is actually 16 / 2 (the jump scale for Gen5-7).

v2: Make the helper a static inline defined in brw_eu.h, instead of
    an actual function in brw_eu_emit.c (as suggested by Matt).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Matt Turner <mattst88@gmail.com>