bus: mhi: host: Refactor BHI/BHIe based firmware loading

Refactor the firmware loading code to have distinct helper functions for
BHI and BHIe operations. This lays the foundation for separating the
firmware loading protocol from the firmware being loaded and the EE it
is loaded in.

Signed-off-by: Matthew Leung <quic_mattleun@quicinc.com>
Reviewed-by: Youssef Samir <quic_yabdulra@quicinc.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250117170943.2643280-2-quic_jhugo@quicinc.com