mmc: sunxi: Disable irq during pm_suspend

When mmc host controller enters suspend state, the clocks are
disabled, but irqs are not. For some reason the irqchip emits
false interrupts, which causes system lock loop.

Debug log is:
  ...
  sunxi-mmc 1c11000.mmc: setting clk to 52000000, rounded 51200000
  sunxi-mmc 1c11000.mmc: enabling the clock
  sunxi-mmc 1c11000.mmc: cmd 13(8000014d) arg 10000 ie 0x0000bbc6 len 0
  sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
  sunxi-mmc 1c11000.mmc: cmd 6(80000146) arg 3210101 ie 0x0000bbc6 len 0
  sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
  sunxi-mmc 1c11000.mmc: cmd 13(8000014d) arg 10000 ie 0x0000bbc6 len 0
  sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00000004 idi 00000000
  mmc1: new DDR MMC card at address 0001
  mmcblk1: mmc1:0001 AGND3R 14.6 GiB
  mmcblk1boot0: mmc1:0001 AGND3R partition 1 4.00 MiB
  mmcblk1boot1: mmc1:0001 AGND3R partition 2 4.00 MiB
  sunxi-mmc 1c11000.mmc: cmd 18(80003352) arg 0 ie 0x0000fbc2 len 409
  sunxi-mmc 1c11000.mmc: irq: rq (ptrval) mi 00004000 idi 00000002
   mmcblk1: p1
  sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
  sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
  sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
  sunxi-mmc 1c11000.mmc: irq: rq   (null) mi 00000000 idi 00000000
and so on...

This issue apears on eMMC cards, routed on MMC2 slot. The patch is
tested with A20-OLinuXino-MICRO/LIME/LIME2 boards.

Fixes: 9a8e1e8c ("mmc: sunxi: Add runtime_pm support")
Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>