ARM: shmobile: Remove unused dma-register.h

The last users of "dma-register.h" were the sh73a0 and r8a7740 legacy
SoC code, which have been removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>