mmc: sd: add support for signal voltage switch procedure

Host Controller v3.00 adds another Capabilities register. Apart
from other things, this new register indicates whether the Host
Controller supports SDR50, SDR104, and DDR50 UHS-I modes. The spec
doesn't mention about explicit support for SDR12 and SDR25 UHS-I
modes, so the Host Controller v3.00 should support them by default.
Also if the controller supports SDR104 mode, it will also support
SDR50 mode as well. So depending on the host support, we set the
corresponding MMC_CAP_* flags. One more new register. Host Control2
is added in v3.00, which is used during Signal Voltage Switch
procedure described below.

Since as per v3.00 spec, UHS-I supported hosts should set S18R
to 1, we set S18R (bit 24) of OCR before sending ACMD41. We also
need to set XPC (bit 28) of OCR in case the host can supply >150mA.
This support is indicated by the Maximum Current Capabilities
register of the Host Controller.

If the response of ACMD41 has both CCS and S18A set, we start the
signal voltage switch procedure, which if successfull, will switch
the card from 3.3V signalling to 1.8V signalling. Signal voltage
switch procedure adds support for a new command CMD11 in the
Physical Layer Spec v3.01. As part of this procedure, we need to
set 1.8V Signalling Enable (bit 3) of Host Control2 register, which
if remains set after 5ms, means the switch to 1.8V signalling is
successfull. Otherwise, we clear bit 24 of OCR and retry the
initialization sequence. When we remove the card, and insert the
same or another card, we need to make sure that we start with 3.3V
signalling voltage. So we call mmc_set_signal_voltage() with
MMC_SIGNAL_VOLTAGE_330 set so that we are back to 3.3V signalling
voltage before we actually start initializing the card.

Tested by Zhangfei Gao with a Toshiba uhs card and general hs card,
on mmp2 in SDMA mode.

Signed-off-by: Arindam Nath <arindam.nath@amd.com>
Reviewed-by: Philip Rakity <prakity@marvell.com>
Tested-by: Philip Rakity <prakity@marvell.com>
Acked-by: Zhangfei Gao <zhangfei.gao@marvell.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

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