[ARM] 2911/1: ixp2000_reg_{read,write} accessors

[ARM] 2911/1: ixp2000_reg_{read,write} accessors

Patch from Lennert Buytenhek

This patch:
- changes the ixp2000_reg_write accessor to take a 'volatile void *'
  instead of a 'volatile unsigned long *', which then allows passing in
  a u32 * as first argument without being greeted with a warning; and
- adds an ixp2000_reg_read accessor.
We can then use these accessors in ixp2000 code to access on-chip
peripherals, instead of directly dereferencing pointers.  This is for
use by the ixp2000 microengine driver which was recently announced on
netdev.  We can't use readl/writel on the ixp2000 since it is usually
run in big-endian mode, and on big-endian platforms, readl/writel
perform byteswapping.
A future patch will remove the readback from ixp2000_reg_write, since
it's not needed to prevent erratum #66, and add manual readbacks to the
places that need them (writes are not synchronous since we map in device
space using XCB=101 nowadays), such as interrupt disabling and GPIO
manipulation.  See also:
	http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2005-February/027084.html
Patch has been ACKed by Jeff Garzik.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>