Stellaris: Implement set_address() and readn() in LPC driver

Although readn() is implemented, a mechanism to bulk read the chip is not
implemented in this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Stellaris: Print error code when control request isn't handled

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>