board: samsung: add support for Galaxy A series of 2017 (a5y17lte)

Samsung Galaxy A3, A5, A7 (2017) - middle class Samsung smartphones.
U-boot can be used as chain-loaded bootloader to gain control
on booting vanilla linux(and possibly others) kernels

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>