GMAC: add driver for Rockchip RK3288 SoCs integrated GMAC

This driver is based on stmmac driver.

changes since v2:
- use tab instead of space for macros
- use HIWORD_UPDATE macro for GMAC_CLK_RX_DL_CFG and GMAC_CLK_TX_DL_CFG
- remove drive-strength setting in the driver and set it in the pinctrl settings
- use dev_err instead of pr_err
- remove clock names's macros, just use the real name of the clock
- use devm_clk_get() instead of clk_get()
- remove clk_set_parent(bsp_priv->clk_mac, bsp_priv->clk_mac_pll)
- remove gpio setting for LDO, just use regulator API
- remove phy reset using gpio in the glue layer, it has been handled in the stmmac driver
- remove handling phy interrupt (mii interrupt)

changes since v1:
- use BIT() to set register
- combine two remap_write() operations into one for the same register
- use macros for register value setting
- remove grf fail check in rk_gmac_setup() and save all the check in set_rgmii_speed()
- remove .tx_coe=1 in rk_gmac_data

Signed-off-by: Roger Chen <roger.chen@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>