i2c, bootcount: add support for bootcounter on i2c devices

add support for bootcounter on an i2c device. And add a
README for all bootcounter options.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/bootcount/Makefile b/drivers/bootcount/Makefile
index bed6971..6f1c419 100644
--- a/drivers/bootcount/Makefile
+++ b/drivers/bootcount/Makefile
@@ -9,3 +9,4 @@
 obj-$(CONFIG_BOOTCOUNT_AM33XX)	+= bootcount_davinci.o
 obj-$(CONFIG_BOOTCOUNT_RAM)	+= bootcount_ram.o
 obj-$(CONFIG_BOOTCOUNT_ENV)	+= bootcount_env.o
+obj-$(CONFIG_BOOTCOUNT_I2C)	+= bootcount_i2c.o