eeprom: Zap CONFIG_SYS_I2C_MULTI_EEPROMS

This option only complicates the code unnecessarily, just use
CONFIG_SYS_DEF_EEPROM_ADDR as the default address if there are
only five arguments to eeprom {read/write} if this is defined.
If CONFIG_SYS_DEF_EEPROM_ADDR is not defined, we mandate all
six arguments.

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>