sunxi: A64: fix default DRAM_ODT_EN symbol

sunxi: A64: fix default DRAM_ODT_EN symbol

"default" lines in Kconfig are processed in order, the first hit will
stop considering subsequent lines. In the case of the DRAM_ODT_EN symbol
that means that everything following the first two lines will never be
checked:
------------
config DRAM_ODT_EN
	bool "sunxi dram odt enable"
	default n if !MACH_SUN8I_A23
	default y if MACH_SUN8I_A23
	default y if MACH_SUN8I_R40
	default y if MACH_SUN50I
------------

Assuming that the "default y" for the A64 and the R40 were a deliberate
choice, fix the Kconfig stanza to take this into account.
Also remove the now redundant lines from the respective defconfigs.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[jagan: droped 'default n' on original change]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # A64, R40
Tested-by: Chen-Yu Tsai <wens@csie.org> # A23