Convert CONFIG_FSL_IIM to Kconfig

This converts the following to Kconfig:
   CONFIG_FSL_IIM

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/doc/README.fsl_iim b/doc/README.fsl_iim
index e087f5e..78d3cb8 100644
--- a/doc/README.fsl_iim
+++ b/doc/README.fsl_iim
@@ -45,4 +45,4 @@
 Configuration:
 
    CONFIG_FSL_IIM
-      Define this to enable the fsl_iim driver.
+      Enable this to enable the fsl_iim driver.