ARM: sunxi: enable big-endian

With previous fixes to stmmac, sun4i-emac and sun4i-mmc at least the
Cubieboard2 incarnation of sunxi works correctly in big-endian mode.
Allow the selection of big-endian.

Tested using a Cubieboard2 DualCard and the following
hardware-components:
- GMAC (stmmac)
- EMAC (sun4i-emac)
- SATA
- SPI
- UART
- security system
- touchscreen controller hwmon functionality
- pinctrl (custom interrupt for SPI ethernet controller)
- watchdog as reset controller
- onboard RTC
- DS1307 I2C RTC
- sound codec and with this indirectly the DMA engine

Signed-off-by: Michael Weiser <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Chen-Yu Tsai <[e-mail]>
Cc: [e-mail]
Signed-off-by: Maxime Ripard <[e-mail]>

arch/arm/mach-sunxi/Kconfig

···
 	default ARCH_SUNXI
 	select ARM_GIC
 	select ARM_PSCI
+	select ARCH_SUPPORTS_BIG_ENDIAN
 	select HAVE_ARM_ARCH_TIMER
 	select SUN5I_HSTIMER