sunxi: Move common defconfig options to Kconfig

Some config symbols are found in *almost* every _defconfig file for
Allwinner boards, because those options are actually a platform choice,
and not a per-board decision.
Some of these options are older, some have recently been added.

Move those options to be set for all Allwinner boards in their
respective Kconfig files.

The rationales are as follows:
- NR_DRAM_BANKS: All Allwinner SoC map DRAM at one contiguous region of
  address space only, starting at 1 GB. So it's always one bank.
- SPL_{DOS,EFI}_PARTITION: The Allwinner SPL does only support raw MMC
  accesses, we don't care about filesystems or partitions in there, so
  there is no need to define those symbols at all.
- USE_PREBOOT: We start USB early when a keyboard is configured, using the
  preboot env variable, so we need to set this variable.
- SYS_RELOC_GD_ENV_ADDR: We don't specify any ENV_ADDR, so need this
  symbol to be set (according to 8d8ee47e03).
- SYS_USB_EVENT_POLL_VIA_INT_QUEUE: According to commit eab9433aa5,
  specifying this reduces the latency of the USB keyboard handling, so
  this was formerly enabled in config headers for all Allwinner boards.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # Amarula A64-Relic
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>

Kconfig

@@ -115,6 +115,7 @@ config ENV_VARS_UBOOT_CONFIG
 
 config NR_DRAM_BANKS
 	int "Number of DRAM banks"
+	default 1 if ARCH_SUNXI
 	default 4
 	help
 	  This defines the number of DRAM banks.