staging/olpc_dcon: fix kconfig to fix build errors

staging/olpc_dcon: fix kconfig to fix build errors

Fix build errors when GPIO_CS5535=m and FB_OLPC_DCON=y
by preventing that kconfig combination.

These build errors are caused by having a kconfig bool symbol
(FB_OLPC_DCON_1) that depend on a tristate symbol (GPIO_CS5535),
but when the tristate symbol is =m, the bool symbol is =y.

  drivers/built-in.o: In function `dcon_read_status_xo_1':
  olpc_dcon_xo_1.c:(.text+0x359531): undefined reference to `cs5535_gpio_set'
  drivers/built-in.o: In function `dcon_wiggle_xo_1':
  olpc_dcon_xo_1.c:(.text+0x35959f): undefined reference to `cs5535_gpio_set'
  olpc_dcon_xo_1.c:(.text+0x359610): undefined reference to `cs5535_gpio_clear'
  drivers/built-in.o:olpc_dcon_xo_1.c:(.text+0x3596a1): more undefined references to `cs5535_gpio_clear' follow
  drivers/built-in.o: In function `dcon_wiggle_xo_1':
  olpc_dcon_xo_1.c:(.text+0x359708): undefined reference to `cs5535_gpio_set'
  drivers/built-in.o: In function `dcon_init_xo_1':
  olpc_dcon_xo_1.c:(.text+0x35989b): undefined reference to `cs5535_gpio_clear'
  olpc_dcon_xo_1.c:(.text+0x3598b5): undefined reference to `cs5535_gpio_isset'
  olpc_dcon_xo_1.c:(.text+0x359963): undefined reference to `cs5535_gpio_setup_event'
  olpc_dcon_xo_1.c:(.text+0x359980): undefined reference to `cs5535_gpio_set_irq'
  olpc_dcon_xo_1.c:(.text+0x359a36): undefined reference to `cs5535_gpio_set'

However, adding GPIO_CS5535 to the Kconfig dependencies also creates
a kconfig recursive dependency error on powerpc:
  drivers/i2c/Kconfig:5:error: recursive dependency detected!
  drivers/i2c/Kconfig:5:	symbol I2C is selected by FB_OLPC_DCON
  drivers/staging/olpc_dcon/Kconfig:1:	symbol FB_OLPC_DCON depends on GPIO_CS5535
  drivers/gpio/Kconfig:577:	symbol GPIO_CS5535 depends on GPIOLIB
  drivers/gpio/Kconfig:38:	symbol GPIOLIB is selected by ARCH_REQUIRE_GPIOLIB
  drivers/gpio/Kconfig:23:	symbol ARCH_REQUIRE_GPIOLIB is selected by MCU_MPC8349EMITX
  arch/powerpc/platforms/Kconfig:351:	symbol MCU_MPC8349EMITX depends on I2C

This is due to FB_OLPC_DCON selecting I2C instead of depending on it,
so change the select to a dependency.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc:	Daniel Drake <dsd@laptop.org>
Cc:	Jens Frederich <jfrederich@gmail.com>
Cc:	Jon Nettleton <jon.nettleton@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>