net: ll_temac: Add LL TEMAC driver to u-boot

Xilinx LocalLink Tri-Mode Ether MAC driver can be
used by Xilinx Microblaze or Xilinx ppc405/440 in
SDMA and FIFO mode. DCR or XPS bus can be used.

The driver uses and requires MII and PHYLIB.

CP: 4 warnings: 'Use of volatile is usually wrong'
I won't fix this, because it depends on the network
driver subsystem.

Reported-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: Stephan Linz <linz@li-pro.net>