sh: remove duplicate ioread/iowrite helpers

sh: remove duplicate ioread/iowrite helpers

The ioread/iowrite functions on sh only do memory mapped I/O like the
generic verion, and never map onto non-MMIO inb/outb variants, so they
just add complexity. In particular, the use of asm-generic/iomap.h
ties the declaration to the x86 implementation.

Remove the custom versions and use the architecture-independent fallback
code instead. Some of the calling conventions on sh are different here,
so fix that by adding 'volatile' keywords where required by the generic
implementation and change the cpg clock driver to no longer depend on
the interesting choice of return types for ioread8/ioread16/ioread32.

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