Fix various typos, scattered over the code.

Spelling corrections for (among other things):

* environment
* override
* variable
* ftd (should be "fdt", for flattened device tree)
* embedded
* FTDI
* emulation
* controller
diff --git a/board/freescale/mx28evk/README b/board/freescale/mx28evk/README
index a248fb2..b8bee89 100644
--- a/board/freescale/mx28evk/README
+++ b/board/freescale/mx28evk/README
@@ -45,7 +45,7 @@
 
 or
 
-"make mx28evk_spi_config"       - store enviroment variables into SPI NOR flash
+"make mx28evk_spi_config"       - store environment variables into SPI NOR flash
 
 Choose the target accordingly.