mdss: mdp: print warning only once for prefetch configuration

control setup gets called for every suspend/resume and this warning
message is printed everytime. Hence, print panel's vfp related warning
message only once.

Change-Id: I4deb0d5faafca1f34a35fc37686bb55d8cbe02e5
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>