bus: mhi: core: Set BHI/BHIe offsets on power up preparation

Set the BHI and/or BHIe offsets in mhi_prepare_for_power_up(),
rearrange the function, and remove the equivalent from
mhi_async_power_up(). This helps consolidate multiple checks
in different parts of the driver and can help MHI fail early on
before power up begins if the offsets are not read correctly.

Link: https://lore.kernel.org/r/1620330705-40192-2-git-send-email-bbhatt@codeaurora.org
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bhaumik Bhatt <bbhatt@codeaurora.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20210802051255.5771-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>