mmc: sdhci-pci-gli: fix LPM negotiation so x86/S0ix SoCs can suspend

To improve the r/w performance of GL9763E, the current driver inhibits LPM
negotiation while the device is active.

This prevents a large number of SoCs from suspending, notably x86 systems
which commonly use S0ix as the suspend mechanism - for example, Intel
Alder Lake and Raptor Lake processors.

Failure description:
1. Userspace initiates s2idle suspend (e.g. via writing to
   /sys/power/state)
2. This switches the runtime_pm device state to active, which disables
   LPM negotiation, then calls the "regular" suspend callback
3. With LPM negotiation disabled, the bus cannot enter low-power state
4. On a large number of SoCs, if the bus not in a low-power state, S0ix
   cannot be entered, which in turn prevents the SoC from entering
   suspend.

Fix by re-enabling LPM negotiation in the device's suspend callback.

Suggested-by: Stanislaw Kardach <skardach@google.com>
Fixes: f9e5b33934ce ("mmc: host: Improve I/O read/write performance for GL9763E")
Cc: stable@vger.kernel.org
Signed-off-by: Sven van Ashbrook <svenva@chromium.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230831160055.v3.1.I7ed1ca09797be2dd76ca914c57d88b32d24dac88@changeid
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>