hexagon: Don't select GENERIC_IOMAP without HAS_IOPORT support

In a future patch HAS_IOPORT=n will disable inb()/outb() and friends at
compile time. As hexagon does not support I/O port access it also
the GENERIC_IOMAP mechanism of dynamically choosing between I/O port and
MMIO access doesn't work so don't select it.

Reviewed-by: Brian Cain <bcain@quicinc.com>
Co-developed-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>