eeprom: refactor i2c bus and devaddr parsing

eeprom: refactor i2c bus and devaddr parsing

Introduce parse_i2c_bus_addr() to generalize the parsing of i2c bus number and
i2c device address. This is done in preparation for merging layout aware and
layout unaware command parsing into one function.

No functional changes.

Cc: Heiko Schocher <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Igor Grinberg <[email protected]>
Cc: Tom Rini <[email protected]>
Signed-off-by: Nikita Kiryanov <[email protected]>