Add SH1106 OLED support (#5787)

* modify oled_driver to support SH1106

also:
- improve mechanism to specify which OLED IC we use
- comment calc_bounds()
- give OLED_COLUMN_OFFSET a default value
- inline comment re: OLED MEMORY_MODE and SH1106
- update docs/feature_oled_driver.h for SH1106 support and related changes
- docs: OLED: note we have tested SSD1306 on ARM boards (per @XScorpion2)
- define out MEMORY_MODE when using SH1106 OLED driver

* document that SSD1306 128x64 on AVR works

Per @XScorpion2: https://github.com/qmk/qmk_firmware/pull/5787#discussion_r291837842

drivers/oled/oled_driver.h

@@ -19,6 +19,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <stdint.h>
 #include <stdbool.h>
 
+// an enumeration of the chips this driver supports
+#define OLED_IC_SSD1306 0
+#define OLED_IC_SH1106  1
 
 #if defined(OLED_DISPLAY_CUSTOM)
   // Expected user to implement the necessary defines
@@ -100,7 +103,16 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
   // #define OLED_TARGET_MAP { 48, 32, 16, 0, 56, 40, 24, 8 }
 #endif // defined(OLED_DISPLAY_CUSTOM)
 
-// Address to use for tthe i2d oled communication
+#if !defined(OLED_IC)
+  #define OLED_IC OLED_IC_SSD1306
+#endif
+
+// the column address corresponding to the first column in the display hardware
+#if !defined(OLED_COLUMN_OFFSET)
+  #define OLED_COLUMN_OFFSET 0
+#endif
+
+// Address to use for the i2c oled communication
 #if !defined(OLED_DISPLAY_ADDRESS)
   #define OLED_DISPLAY_ADDRESS 0x3C
 #endif