ARM: OMAP2+: Remove MACH_NOKIA_N800

The last caller of machine_is_nokia_n800() was removed in commit
5a87cde490e1 ("ARM: OMAP2+: Remove legacy booting support for n8x0").
That means that the Kconfig symbol MACH_NOKIA_N800 is now unused. It can
safely be removed.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>