mmc: core: Add wp_grp_size sysfs node

mmc: core: Add wp_grp_size sysfs node

The eMMC card can be set into write-protected mode to prevent data from
being accidentally modified or deleted. Wp_grp_size (Write Protect Group
Size) refers to an attribute of the eMMC card, used to manage write
protection and is the CSD register [36:32] of the eMMC device. Wp_grp_size
(Write Protect Group Size) indicates how many eMMC blocks are contained in
each write protection group on the eMMC card.

To allow userspace easy access of the CSD register bits, let's add sysfs
node "wp_grp_size".

Signed-off-by: Lin Gui <lin.gui@mediatek.com>
Signed-off-by: Bo Ye <bo.ye@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20231218230532.82427-1-bo.ye@mediatek.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>