drivers/ide/pci/generic: fix build for CONFIG_HOTPLUG=n

It turns out that const and __{dev}initdata cannot be mixed currently
and that generic IDE PCI host driver is also affected by the same issue:

On Thursday 25 October 2007, Ralf Baechle wrote:
>   CC      drivers/ide/pci/generic.o
> drivers/ide/pci/generic.c:52: error: __setup_str_ide_generic_all_on causes a
> +section type conflict

[ Also reported by Martijn Uffing <mp3project@sarijopen.student.utwente.nl>. ]

This patch workarounds the problem in a bit hackish way but without
removing const from generic_chipsets[] (it adds const to __setup() so
__setup_str_ide_generic_all becomes const).

Now all __{dev}initdata data in generic IDE PCI host driver are read-only
so it builds again (driver's .init.data section gets marked as READONLY).

Cc: Martijn Uffing <mp3project@sarijopen.student.utwente.nl>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>