mmc: octeontx2: skip unavailable slots

commit c9222d396d1d9e7095d1aef64b437462547ce3e7 from
git@git.assembla.com:cavium/WindRiver.linux.git

Skip devtree mmc-slot nodes marked unavailable
(those with a status property that is not "ok")

Note that a missing 'status' property marks the node
available, nothing need be added to activate it.

This allows multiple alternate entries in firmware
devtree, with dormant nodes marked (eg) status="off",
to be boot-time enabled without rewriting the whole fdt,
by simple u-boot commands like
  fdt rm $mmc/mmc-slot@2 status
enabling an mmc2 entry that is normally disabled

Change-Id: Ib680a2bc1dd58bebaabcbb47f2560c00f32ab250
Signed-off-by: Peter Swain <pswain@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <Sunil.Goutham@cavium.com>
Reviewed-on: https://sj1git1.cavium.com/8544


Tested-by: Sunil Kovvuri Goutham <Sunil.Goutham@cavium.com>
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/26906


Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>