kbuild: frv,m32r,sparc64 introduce fake asm-offsets.h file

Needed to get them to build.
And a hint to avoid hardcoding to many constants in assembler.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/frv/kernel/asm-offsets.c

+/* Dummy asm-offsets.c file. Required by kbuild and ready to be used - hint! */

arch/m32r/kernel/asm-offsets.c

+/* Dummy asm-offsets.c file. Required by kbuild and ready to be used - hint! */

arch/sparc64/kernel/asm-offsets.c

+/* Dummy asm-offsets.c file. Required by kbuild and ready to be used - hint! */