msm: ipa: add an API to check if IPA driver is ready

Clients can use this API to ensure IPA driver was
initialized successfully before invoking any other IPA APIs.

Change-Id: Ib4a8b62a2c9a2746db1090f540cccd01bae74272
Signed-off-by: Ravi Gummadidala <rgummadi@codeaurora.org>