powerpc: asm/io.h: remove split ioread64/iowrite64 helpers

powerpc: asm/io.h: remove split ioread64/iowrite64 helpers

In previous kernels, there were conflicting definitions for what
ioread64_lo_hi() and similar functions were supposed to do on
architectures with native 64-bit MMIO. Based on the actual usage in
drivers, they are in fact expected to be a pair of 32-bit accesses on
all architectures, which makes the powerpc64 definition wrong.

Remove it and use the generic implementation instead.

Drivers that want to have split lo/hi or hi/lo accesses on 32-bit
architectures but can use 64-bit accesses where supported should instead
use ioread64()/iowrite64() after including the corresponding header file.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>