bus: mhi: core: Improve state strings for debug messages

As of now abbreviations are being used for many state and
execution environment strings. Improve and expand those such that
debug messages are clear.

Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Link: https://lore.kernel.org/r/1617067704-28850-8-git-send-email-bbhatt@codeaurora.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>