I started with Yocto Jethro, and I successfully built a system image with the new 4.1 kernel.
I customized it with device tree, but I'm stuck with network. Our design use LAN8720 like Auto EVB, but RMII clock is provided by CKO1 output, CKO1(PTB10) is connected to RMII_CLKIN (PTA6) and connected to LAN8720 CLKIN (see this). This design needs few BSP customizations and it worked fine with the old 3.0.15 kernel from Timesys.
PTB10 is well configured as CKO1 mode by device tree, and CCSOR, PLL5_CTRL configured by u-boot.
At the end of kernel init, just before rfs mount, RMII CLK stops, then eth0 becomes unavailable.
But I don't know if PTB10 iomux mode changed or CCSOR/PLL5_CTRL.