arm/aspeed: rainier: Add i2c eeproms and muxes

arm/aspeed: rainier: Add i2c eeproms and muxes

These are the devices documented by the Rainier device tree. With this
we can see the guest discovering the multiplexers and probing the eeprom
devices:

 i2c i2c-2: Added multiplexed i2c bus 16
 i2c i2c-2: Added multiplexed i2c bus 17
 i2c i2c-2: Added multiplexed i2c bus 18
 i2c i2c-2: Added multiplexed i2c bus 19
 i2c-mux-gpio i2cmux: 4 port mux on 1e78a180.i2c-bus adapter
 at24 20-0050: 8192 byte 24c64 EEPROM, writable, 1 bytes/write
 i2c i2c-4: Added multiplexed i2c bus 20
 at24 21-0051: 8192 byte 24c64 EEPROM, writable, 1 bytes/write
 i2c i2c-4: Added multiplexed i2c bus 21
 at24 22-0052: 8192 byte 24c64 EEPROM, writable, 1 bytes/write

Signed-off-by: Joel Stanley <joel@jms.id.au>
[ clg: Introduced aspeed_eeprom_init ]
Message-Id: <20210629142336.750058-2-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>