sunxi: Make DRAM_ODT_EN Kconfig setting a bool

Make DRAM_ODT_EN Kconfig setting a bool, add a separate DRAM_ODT_CORRECTION
setting for A23 SoCs and use DRAM_ODT_EN Kconfig everywhere instead of
only in dram_sun4i.c and hardcoding odt_en elsewhere.

Note this commit makes no functional changes for existing boards,
its purpose is to allow changing the odt_en value on future A33 boards.

For sun4i/sun5i/sun7i boards which set DRAM_ODT_EN=y (which no defconfigs
currently do) this patch turns on odt for both the DQ and the DQS lines,
whereas previously it was possibly (but not desirable) to turn odt on only
for one of them by setting the in DRAM_ODT_EN option to 1 or 2 instead of 3.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>