arm: K3: sysfw-loader: Add a config_pm_pre_callback()

System firmware does not guarantee that clocks going out of the device
will be stable during power management configuration. There are some
DCRC errors when SPL tries to get the next stage during eMMC boot after
sysfw pm configuration.

Therefore add a config_pm_pre_callback() to switch off the eMMC clock
before power management and restart it after it is done.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>