EFM32 Wonder Gecko Family support

Add support for EFM32 Wonder Gecko family to flash driver.
This family has Cortex M4F core.

Change-Id: If71511015403069e3e30cb9f19df12cd97ac49e8
Signed-off-by: Joerg Fischer <turboj@gmx.de>
Reviewed-on: http://openocd.zylin.com/1968


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>