ARC: Move ENV_SIZE and ENV_OFFSET to Kconfig

Join the party of some ARM boards and drop more
items from include/configs/xxx.h.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>