kbuild: allow assignment to {A,C,LD}FLAGS_MODULE on the command line

kbuild: allow assignment to {A,C,LD}FLAGS_MODULE on the command line

It is now possible to assign options to AS, CC and LD
on the command line - which is only used when building modules.

{A,C,LD}FLAGS_MODULE was all used both in the top-level Makefile
in the arch makefiles, thus users had no way to specify
additional options to AS, CC, LD when building modules
without overriding the original value.

Introduce a new set of variables KBUILD_{A,C,LD}FLAGS_MODULE
that is used by arch specific files and free up
{A,C,LD}FLAGS_MODULE so they can be assigned on
the command line.

All arch Makefiles that used the old variables has been updated.

Note: Previously we had a MODFLAGS variable for both
AS and CC. But in favour of consistency this was dropped.
So in some cases arch Makefile has one assignmnet replaced by
two assignmnets.

Note2: MODFLAGS was not documented and is dropped
without any notice. I do not expect much/any breakage
from this.

Signed-off-by: Sam Ravnborg <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Haavard Skinnemoen <[email protected]>
Cc: Mike Frysinger <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Chen Liqin <[email protected]>
Acked-by: Mike Frysinger <[email protected]> [blackfin]
Acked-by: Haavard Skinnemoen <[email protected]> [avr32]
Signed-off-by: Michal Marek <[email protected]>