hwmon: Avoid building drivers for powerpc that read/write ISA addresses

A modprobe of hwmon drivers that read/write ISA addresses on a powerpc results
in a kernel Oops. These reads/writes are being done via the inb()/in_8() and
outb()/out_8() macros.

Prevent these drivers from being built for powerpc.

Signed-off-by: Dean Nelson <dnelson@redhat.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>