boards/shields: ssd1306: Factorize and move to conditional Kconfig

Factorize definitions for ssd1306_128x32 and sd1306_128x64 shields
and move to conditional Kconfig.
As part of this change, direct drivers Kconfig symbols enabling
(I2C, SSD1306) are removed as they are application responsibility.
Also disabling SSD16XX is removed as SSD16XX should not be enabled
by default.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>