ARM: OMAP1: fix compilation issue in board-sx1.c

SX1 board requirese i2c, so select it in Kconfig, otherwise I have the
following build error:

arch/arm/mach-omap1/board-sx1.c: In function 'sx1_i2c_write_byte':
arch/arm/mach-omap1/board-sx1.c:58:2: error: implicit declaration of function 'i2c_get_adapter' [-Werror=implicit-function-declaration]
arch/arm/mach-omap1/board-sx1.c:58:7: warning: assignment makes pointer from integer without a cast [enabled by default]
arch/arm/mach-omap1/board-sx1.c:67:2: error: implicit declaration of function 'i2c_transfer' [-Werror=implicit-function-declaration]
arch/arm/mach-omap1/board-sx1.c:68:2: error: implicit declaration of function 'i2c_put_adapter' [-Werror=implicit-function-declaration]
arch/arm/mach-omap1/board-sx1.c: In function 'sx1_i2c_read_byte':
arch/arm/mach-omap1/board-sx1.c:82:7: warning: assignment makes pointer from integer without a cast [enabled by default]
cc1: some warnings being treated as errors
make[1]: *** [arch/arm/mach-omap1/board-sx1.o] Error 1
make: *** [arch/arm/mach-omap1] Error 2
make: *** Waiting for unfinished jobs....

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>