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/Kconfig b/drivers/spi/Kconfig
index 15207d2..098372e 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -213,6 +213,13 @@
 		};
 	  };
 
+config SPI_SUNXI
+	bool "Allwinner SoC SPI controllers"
+	help
+	  Enable the Allwinner SoC SPi controller driver.
+
+	  Same controller driver can reuse in all Allwinner SoC variants.
+
 config STM32_QSPI
 	bool "STM32F7 QSPI driver"
 	depends on STM32F7
@@ -222,11 +229,6 @@
 	  used to access the SPI NOR flash chips on platforms embedding
 	  this ST IP core.
 
-config SUN4I_SPI
-	bool "Allwinner A10/A31 SoCs SPI controller"
-	help
-	  This enables using the SPI controller on the Allwinner A10/A31 SoCs.
-
 config TEGRA114_SPI
 	bool "nVidia Tegra114 SPI driver"
 	help