Merge remote-tracking branch 'remotes/cminyard/tags/for-qemu-i2c-5' into staging

Minor changes to:

Add an SMBus config entry

Cleanup/simplify/document some I2C interfaces

# gpg: Signature made Thu 16 Jul 2020 18:46:55 BST
# gpg:                using RSA key FD0D5CE67CE0F59A6688268661F38C90919BFF81
# gpg: Good signature from "Corey Minyard <cminyard@mvista.com>" [unknown]
# gpg:                 aka "Corey Minyard <minyard@acm.org>" [unknown]
# gpg:                 aka "Corey Minyard <corey@minyard.net>" [unknown]
# gpg:                 aka "Corey Minyard <minyard@mvista.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: FD0D 5CE6 7CE0 F59A 6688  2686 61F3 8C90 919B FF81

* remotes/cminyard/tags/for-qemu-i2c-5:
  hw/i2c: Document the I2C qdev helpers
  hw/i2c: Rename i2c_create_slave() as i2c_slave_create_simple()
  hw/i2c: Rename i2c_realize_and_unref() as i2c_slave_realize_and_unref()
  hw/i2c: Rename i2c_try_create_slave() as i2c_slave_new()
  hw/i2c/aspeed_i2c: Simplify aspeed_i2c_get_bus()
  hw/i2c/Kconfig: Add an entry for the SMBus

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>