mmc: core: increase delay between power-up and power-on

Add a capability to selectively increase the delay between
power_up and power_on. This delay was arrived at after performing
a series of experiments to find the minimum value. It is required
in some scenarios to avoid command timeouts during resume.

Change-Id: I857e740aa20a33e08515d054e5c9bf128db229c6
Signed-off-by: Guoping Yu <guopingy@codeaurora.org>