msm: ecm_ipa: add debug ability to manually stall IPA core

This change add the ability to cause IPA core simulate
a stall. this adds the ability to debug and analyze issues that
only happen during data stall.
There is no functional change to the driver and this feature
is only used for debugging.

Change-Id: I12f5db9809f8a16ebe23751197925c4d380aac81
Signed-off-by: Talel Shenhar <tatias@codeaurora.org>