dmaengine: rcar-dmac: don't use DMAC error interrupt

rcar-dmac has 2 types of interrupt, 1) error IRQ (for all),
2) IRQ for each channels.
If error happens on some channels, the error IRQ will be handled
by 1), and "all" channels will be restarted.
But in this design, error handling itself will be problem for
non error channel users.
This patch removes 1) handler, and handles error IRQ on 2)

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
[Kuninori: updated patch to adjust DMACHCR/DMAOR]
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Nguyen Viet Dung <nv-dung@jinso.co.jp>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Vinod Koul <vkoul@kernel.org>