mmc: tmio: Add MMC_CAP_ERASE to allow erase/discard/trim requests

Isolated initially to renesas_sdhi_internal_dmac [1], Ulf suggested
adding MMC_CAP_ERASE to the TMIO mmc core:

On Fri, Nov 15, 2019 at 10:27:25AM +0100, Ulf Hansson wrote:
 -- snip --
 This test and due to the discussions with Wolfram and you in this
 thread, I would actually suggest that you enable MMC_CAP_ERASE for all
 tmio variants, rather than just for this particular one.

 In other words, set the cap in tmio_mmc_host_probe() should be fine,
 as it seems none of the tmio variants supports HW busy detection at
 this point.
 -- snip --

Testing on R-Car H3ULCB-KF doesn't reveal any issues (v5.4-rc7):

root@rcar-gen3:~# lsblk
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
mmcblk0      179:0    0 59.2G  0 disk  <--- eMMC
mmcblk0boot0 179:8    0    4M  1 disk
mmcblk0boot1 179:16   0    4M  1 disk
mmcblk1      179:24   0   30G  0 disk  <--- SD card

root@rcar-gen3:~# time blkdiscard /dev/mmcblk0
real    0m8.659s
user    0m0.001s
sys     0m1.920s

root@rcar-gen3:~# time blkdiscard /dev/mmcblk1
real    0m1.176s
user    0m0.001s
sys     0m0.124s

[1] https://lore.kernel.org/linux-renesas-soc/20191112134808.23546-1-erosca@de.adit-jv.com/

Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Originally-by: Harish Jenny K N <harish_kandiga@mentor.com>
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/tmio_mmc_core.c

@@ -1184,7 +1184,7 @@ int tmio_mmc_host_probe(struct tmio_mmc_host *_host)
 	if (ret == -EPROBE_DEFER)
 		return ret;
 
-	mmc->caps |= MMC_CAP_4_BIT_DATA | pdata->capabilities;
+	mmc->caps |= MMC_CAP_ERASE | MMC_CAP_4_BIT_DATA | pdata->capabilities;
 	mmc->caps2 |= pdata->capabilities2;
 	mmc->max_segs = pdata->max_segs ? : 32;
 	mmc->max_blk_size = TMIO_MAX_BLK_SIZE;