cmd_i2c: Provide option for bulk 'i2c write' in one transaction

cmd_i2c: Provide option for bulk 'i2c write' in one transaction

I2C chips do exist that require a write of some multi-byte data to occur in
a single bus transaction (aka atomic transfer), otherwise either the write
does not come into effect at all, or normal operation of internal circuitry
cannot be guaranteed. The current implementation of the 'i2c write' command
(transfer of multiple bytes from a memory buffer) in fact performs a separate
transaction for each byte to be written and thus cannot support such types of
I2C slave devices.

This patch provides an alternative by allowing 'i2c write' to execute the
write transfer of the given number of bytes in a single bus transaction if
the '-s' option is specified as a final command argument. Else the current
re-addressing method is used.

Signed-off-by: Lubomir Popov <l-popov@ti.com>
hs: adapt to CONFIG_DM_I2C