The SAAR and TAVOREVB machines try to call functions from
the PXAFB frame buffer driver from their platform code,
which only works if that driver is built-in.

This patch ensures that both the generic frame buffer
code and the specific pxafb driver are always enabled
when we build a kernel for one of the two boards.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Eric Miao <eric.y.miao@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: Daniel Mack <zonque@gmail.com>