Set default OLED Update Interval for Split Keyboards (qmk#12107)

Because the matrix scanning is slower for splits, in general,
the frequent updating of the OLEDs can slow down the matrix scanning.
To help prevent that, set the update interval for the OLEDs to not
update as frequently.

drivers/oled/oled_driver.h

@@ -158,6 +158,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #    define OLED_I2C_TIMEOUT 100
 #endif
 
+#if !defined(OLED_UPDATE_INTERVAL) && defined(SPLIT_KEYBOARD)
+#    define OLED_UPDATE_INTERVAL 50
+#endif
+
 typedef struct __attribute__((__packed__)) {
     uint8_t *current_element;
     uint16_t remaining_element_count;