ARM: hikey: Remove resetting gd->flags in board_init()

This causes exceptions and other strange behaviour
when enabling CONFIG_SYS_MALLOC_F_LEN which is required to
migrate the serial driver over to DM_SERIAL.

As GD_FLG_FULL_MALLOC_INIT flag gets reset, after relocation
we don't end up using the full malloc which ultimately ends up
causing a synchronus abort.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>