soc-family: fix SOC_FAMILY override order

soc-family: fix SOC_FAMILY override order

* the current order has SOC_FAMILY settings, which are generic
  settings for a group of devices, overriding the machine specific
  settings.  For example:

  KERNEL_DEVICETREE_ti33x = "xxxx"
  KERNEL_DEVICETREE_beaglebone = "yyyy"

  Should yield "yyyy" when building for the beaglebone because
  that is a more specific device than ti33x.  However, without this
  change the result is that the value is set to "xxxx" meaning the
  more generic setting overrides the more specific setting.

(From OE-Core rev: 0b836b9d79255a5b2f358fe718c67638f52ecf72)

Signed-off-by: Chase Maupin <Chase.Maupin@ti.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>