bus: mhi: core: Use appropriate names for firmware load functions
mhi_fw_load_sbl() function is currently used to transfer SBL or EDL
images over BHI (Boot Host Interface). Same goes with mhi_fw_load_amss()
which uses BHIe. However, the contents of these functions do not
indicate support for a specific set of images. Since these can be used
for any image download over BHI or BHIe, rename them based on the
protocol used.