As of commit 4baadb9e ("ARM: shmobile: r8a7778: remove obsolete
setup code"), the Renesas R-Car HPB-DMAC driver is no longer used.
In theory it could still be used on R-Car Gen1 SoCs, but that requires
adding DT support to the driver, which is not planned.

Remove the driver, it can be resurrected from git history when needed.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>