UAPI: Rearrange definition of HZ in asm-generic/param.h

Rearrange the definition of HZ in asm-generic/param.h so that the user-specific
is declared before the kernel-specific one.  We then explicitly #undef the
userspace HZ value and replace it with the kernel HZ value.

This allows the userspace params to be excised into a separate header as part
of the UAPI header split.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>