Several ports (x86-64,ppc64,sparc64) which do 32bit ioctl emulation
have functions for drivers to let them define their own translation
handlers. So far it was a bit complicated to use because there
was no standard include file that declares the prototypes for this
stuff. Then drivers and other subsystems can start to declare their own
ioctl translation handlers.

This patch add include/linux/ioctl32.h to fix this.

The actual implementation is in arch specific code. It has been coordinated
with DaveM and Anton.

This patch is needed for the x86-64 merge I sent in separate mail.

There is currently no preprocessor symbol that the drivers can test
to see if they should use this. So far they have to check arch symbols.
This will be fixed later when all 64bit ports that need it add the dynamic
ioctl registration API too (that's ia64,s390x,mips64)