ARM: OMAP2+: Fix unmet direct dependencies for zoom for 8250 serial

We should not select drivers from kconfig as they should by default
be optional. Otherwise we'll be chasing broken dependencies forever:

warning: (MACH_OMAP_ZOOM2 && MACH_OMAP_ZOOM3 && MWAVE) selects SERIAL_8250
which has unmet direct dependencies (TTY && HAS_IOMEM && GENERIC_HARDIRQS)

Fix the issue by removing the selects for zoom and add them to
omap2plus_defconfig.

Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>