[BSP] tm4c129x:
1. Add ETH MAC driver using DMA for Tx and Rx lwip pBuf.
2. Modify the tivaware emac library to fix the bug that PHY read is not stable when sysclk is 120MHz
3. In PHY IRQ handler, insert a dummy reading (REG_BMSR) before read PHY_STS to force update STS register.
Revert "[BSP] tm4c129x:"

This reverts commit 666d12988a2ab3fc9eb878e3b52cb083c85e6dbe.
[BSP] tm4c129x add eth driver
1. Add ETH MAC driver using DMA for Tx and Rx lwip pBuf.
2. Modify the tivaware emac library to fix the bug that PHY read is not stable when sysclk is 120MHz
3. In PHY IRQ handler, insert a dummy reading (REG_BMSR) before read PHY_STS to force update STS register.
[BSP] tm4c129x: fix compile bug when turn  RT_USING_LWIP
1. Resize RT_LWIP_SEG_NUM drom 8 to 12
2. modify gcc compile switch, using C99
Merge pull request #307 from ArdaFu/master

[BSP] tm4c129x Add EMAC/PHY driver