drivers/lcd: ssd1306: separate lcd_dev_s setup to separate object. g_oleddev...

drivers/lcd: ssd1306: separate lcd_dev_s setup to separate object.  g_oleddev takes 1 KiB because framebuffer and was allocated to .data section because of lcd_dev_s function pointer setup. Move lcd_dev_s setup out, so that g_oleddev goes to .bss and avoid wasting ROM.