pnp: increase number of devices supported per protocol

Increase the PNP "number of devices" limit.  We currently use an unsigned
char, which limits us to 256 devices per protocol.  This patch changes that to
an unsigned int.

Not all backends can take advantage of this: we limit ISAPNP to 10 devices in
isapnp_cfg_begin(), and PNPBIOS is limited to 256 devices because the BIOS
interfaces use a one-byte device node number.

But there is no limit on the number of PNPACPI devices we may have.  Large HP
Integrity machines have more than 256, which causes the current "unsigned char
number" to wrap around.  This causes errors like this:

    pnp: PnP ACPI init
    kobject_add failed for 00:00 with -EEXIST, don't try to register things with the same name in the same directory.

    Call Trace:
     [<a000000100010720>] show_stack+0x40/0xa0
     [<a0000001000107b0>] dump_stack+0x30/0x60
     [<a0000001001dbdf0>] kobject_add+0x290/0x2c0
     [<a0000001002bfd40>] device_add+0x160/0x860
     [<a0000001002c0470>] device_register+0x30/0x60
     [<a00000010026ba70>] __pnp_add_device+0x130/0x180
     [<a00000010026bb70>] pnp_add_device+0xb0/0xe0
     [<a0000001007f2730>] pnpacpi_add_device+0x510/0x5a0
     [<a0000001007f2810>] pnpacpi_add_device_handler+0x50/0x80

This patch increases the limit to fix this PNPACPI problem.  It should not
have any adverse effect on ISAPNP or PNPBIOS because their limits are still
enforced in the backends.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>