PCI: epf-mhi: Add "pci_epf_mhi_" prefix to the function names

Without the prefix, the function name would appear as
"/sys/kernel/config/functions/{sdx55/sm8450}". This will be a problem if
multiple functions are supported for this endpoint device.

So let's add the "pci_epf_mhi_" prefix to identify _this_ function
uniquely. Even though it is an ABI breakage, this driver is not used
anywhere outside Qcom and myself to my knowledge. So it safe to change
the function name.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Mrinmay Sarkar <quic_msarkar@quicinc.com>
Link: https://lore.kernel.org/r/1701432377-16899-4-git-send-email-quic_msarkar@quicinc.com