greybus: power_supply: reverse version check for new psy API

Reversing the kernel version check for new power supply APIs will
easily allow us to use older kernels with backported power supply APIs
by defining "CORE_OWNS_PSY_STRUCT" in power supply core header

Testing Done:
- Build tested with arche kernel with backported power supply APIs
- Build tested also with current arche kernel to make sure we build with
  3.10 kernels

Signed-off-by: Sandeep Patil <sspatil@google.com>
Reviewed-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>