mmc: sd: add support for tuning during uhs initialization

Host Controller needs tuning during initialization to operate SDR50
and SDR104 UHS-I cards. Whether SDR50 mode actually needs tuning is
indicated by bit 45 of the Host Controller Capabilities register.
A new command CMD19 has been defined in the Physical Layer spec
v3.01 to request the card to send tuning pattern.

We enable Buffer Read Ready interrupt at the very begining of tuning
procedure, because that is the only interrupt generated by the Host
Controller during tuning. We program the block size to 64 in the
Block Size register. We make sure that DMA Enable and Multi Block
Select in the Transfer Mode register are set to 0 before actually
sending CMD19. The tuning block is sent by the card to the Host
Controller using DAT lines, so we set Data Present Select (bit 5) in
the Command register. The Host Controller is responsible for doing
the verfication of tuning block sent by the card at the hardware
level. After sending CMD19, we wait for Buffer Read Ready interrupt.
In case we don't receive an interrupt after the specified timeout
value, we fall back on fixed sampling clock by setting Execute
Tuning (bit 6) and Sampling Clock Select (bit 7) of Host Control2
register to 0. Before exiting the tuning procedure, we disable Buffer
Read Ready interrupt and re-enable other interrupts.

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>