kbuild: shorthand ym2y, ym2m etc

[Sam Ravnborg <sam@ravnborg.org>]

We have in several cases the need to transpose a i'm' to 'y' in the Kbuild
files.
One example is the following snippet from sound/Makefile:
ifeq ($(CONFIG_SND),y)
  obj-y += last.o
endif

Alternative syntax could be:
obj-$(call y2y,CONFIG_SND) += last.o


y2y takes one parameter and return y unly if parameter is y, otherwise
return nothing.


>From drivers/vidoe/Makfile:
ifeq ($(CONFIG_FB),y)
  obj-$(CONFIG_PPC)                 += macmodes.o
endif

Altetnative syntax:
obj-$(call yx2x,CONFIG_FB,CONFIG_PPC) += mcmodes.o

yx2x return second parameter (x) if first parameter is y. Otherwise
nothing is returned.

To be complete the full set would be:

ym2y
ym2m
empty2y
empty2m
y2y
m2y
y2m
m2m
yx2x
mx2x

Would that be considered usefull?

	Sam