Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Updates for I2C devices on XLR engg boards.

- ds1374u : use multi-byte write.
- at24co2n, max6657: remove mutex, iicbus has the necessary locking.

Submitted by: Sreekanth M. S. (kanthms at netlogicmicro com)

I2C drivers for XLR/XLS processors.

- Major update to xlr_i2c.c: do multi-byte ops correctly, remove unnecessary
code, add mutex to protect bus operations, style(9) fixes.
- Drivers for I2C devices on XLR/XLS engineering boards, ds1374u RTC, max6657
temparature sensor and at24co2n EEPROM.

Submitted by: Sreekanth M. S. (kanthms at netlogicmicro com)