eeprom: Shuffle code around

Just move the code around so that the forward declarations are not
necessary. Also zap a few checkpatch issues where applicable and
zap the use of #ifdef CONFIG_CMD_EEPROM in the code, since this is
always true.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Heiko Schocher <hs@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>