rcar_get3: drivers: ddr: Partly unify register macros between DDR A and B

The ddr_a and ddr_b register macros are the same for the most part,
unify them into a single header.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Change-Id: I8f55d6d779837215339ac0010e8c8ab5f6748d75
7 files changed