mtd: Really add ARM pismo support

(Commit 7cb777a3 (mtd: add ARM pismo support)
intended to add this, but seems only to have patched the Makefile without
touching Kconfig or providing any code...)

The following patch adds support for PISMO modules found on ARM Ltd
development platforms.  These are MTD modules, and can have a
selection of SRAM, flash or DOC devices as described by an on-board
I2C EEPROM.

We support SRAM and NOR flash devices only by registering appropriate
conventional MTD platform devices as children of the 'pismo' device.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>