mmc: cavium: avoid single-slot startup issues

commit 01d87e93c8b7184082a23a8de6438d7711a64d2b from
git@git.assembla.com:cavium/WindRiver.linux.git

Previous code relied on particular state left by u-boot,
or a previous _probe attempt aborted with EPROBE_DEFER,
else it would program a clock-divisor of zero and hang MMC.

Do not cache emm_switch setting if it has clock divisor zero.
Do not use frequency params before they have been extracted
from devtree.
Do enforce lower frequency bound (400KHz) from mmc/core.

Change-Id: I2d19084d1ab57d0f98e2ce1ffcd6fb918228f53c
Signed-off-by: Peter Swain <pswain@marvell.com>
Signed-off-by: Sujeet Baranwal <sbaranwal@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/8549


Tested-by: Sunil Kovvuri Goutham <Sunil.Goutham@cavium.com>
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Signed-off-by: Kevin Hao <kexin.hao@windriver.com>