spi: Rename sun4i_spi.c into spi-sunxi.c

Now the same SPI controller driver is reusable in all Allwinner
SoC variants, so rename the existing sun4i_spi.c into spi-sunxi.c
which eventually look like a common sunxi driver.

Also update the function, variable, structure names in driver from
sun4i into sunxi.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index 3902671..01907be 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -48,10 +48,10 @@
 obj-$(CONFIG_RENESAS_RPC_SPI) += renesas_rpc_spi.o
 obj-$(CONFIG_ROCKCHIP_SPI) += rk_spi.o
 obj-$(CONFIG_SANDBOX_SPI) += sandbox_spi.o
+obj-$(CONFIG_SPI_SUNXI) += spi-sunxi.o
 obj-$(CONFIG_SH_SPI) += sh_spi.o
 obj-$(CONFIG_SH_QSPI) += sh_qspi.o
 obj-$(CONFIG_STM32_QSPI) += stm32_qspi.o
-obj-$(CONFIG_SUN4I_SPI) += sun4i_spi.o
 obj-$(CONFIG_TEGRA114_SPI) += tegra114_spi.o
 obj-$(CONFIG_TEGRA20_SFLASH) += tegra20_sflash.o
 obj-$(CONFIG_TEGRA20_SLINK) += tegra20_slink.o