[PARISC] Add CONFIG_HPPA_IOREMAP to conditionally enable ioremap

Instead of making it a #define in asm/io.h, allow user to select
to turn on IOREMAP from the config menu.

Signed-off-by: Helge Deller <deller@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>