mmc: renesas_internal_dmac: add pre_req and post_req support

Add pre_req and post_req support to improve performance.

Inspired by a patch in the BSP by Masaharu Hayakawa.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/1608114572-1892-3-git-send-email-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>