Introduce env support for sata device.
1. Implement write_env/read_env/env_relocate_spec/saveenv/sata_get_env_dev
2. If want to enable this feature, define CONFIG_ENV_IS_IN_SATA, and
   define CONFIG_SYS_SATA_ENV_DEV or implement your own sata_get_ev_dev.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Stuart Longland <stuartl@vrt.com.au>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>