mmc: sdhci: Defer release of CPU DMA PM QoS vote in high load cases

PM QoS vote of default value mean that the CPU is allowed to move
into deepest low power mode whenever possible. Currently, if there
are back-to-back MMC requests, with a short delay, the PM QoS vote
to default value is done immediately which cause the immediate
request to have high latency as the CPU might have idle'd and moved
to deepest low power mode. To avoid this defer the PM QoS vote till
a defined timeout (pm_qos_timeout_us), so that back-to-back requests
may not suffer from additional latencies.

In addition, if the load on MMC is low, the additional latency may be
sustainable. Hence, aggressively release the vote in order to achieve
additional power savings.

CRs-Fixed: 501712
Change-Id: I82166b0ce9416eb0d519f7da26e5a96956093cb2
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>