i2c: i801: Switch to iomapped register access

Switch to iomapped register access as a prerequisite for adding
support for MMIO register access.

This changes replaces the delayed inb_p()/outb_p() calls with calls to
ioread8()/iowrite8() which don't have this extra delay. According to
Documentation/driver-api/device-io.rst the _p versions are needed
for ISA device access only, therefore switching to the non-delayed
versions should not cause problems. However a certain risk remains,
which on the other hand is significantly reduced by the fact that
recent systems will use MMIO instead of PIO. ICH7 datasheet from 2012
mentions already that SMBus register space is also memory-mapped.
So all systems from at least the last 10 yrs should be safe.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/67535b17-c3fb-4507-b083-9c1884b4dd7d@gmail.com