boards: arm: Add support for STM32F411E-DISCO

Add board configuration, dts and pinmux, based on
arm/stm32f4_disco and arm/nucleo_f411re boards.

Error free tests are executed on eval board with the following
sample applications:

- hello_world
- blinky-sample
- button-sample
- console_echo_sample
- console_getchar_sample

Signed-off-by: Jose F. Fernandez <jffernandez@fenix-es.com>