ARM: stih41x: Add B2020 board support

B2020 ADI board is reference board for STIH415/416 SOCs, it has 2 x
UART, 4x USB, 1 x Ethernet, 1 x SATA, 1 x PCIe, and 2GB RAM  with
standard set-top box IPs.

This patch adds initial support to B2020 with STiH415/416 with SBC_UART1
as console and a heard beat LED.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
CC: Stephen Gallimore <stephen.gallimore@st.com>
CC: Stuart Menefy <stuart.menefy@st.com>
CC: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>