bootloader_utility_load_partition_table() function

Bootloader state structure used to save read data.

Load the selected partition and start application. Start from partition 'start_index', if not bootable then work backwards to FACTORY_INDEX (ie try any OTA slots in descending order and then the factory partition). If still nothing, start from 'start_index + 1' and work up to highest numbered OTA partition. If still nothing, try TEST_APP_INDEX. Everything this function calls must be located in the iram_loader_seg segment.

Return the index of the selected boot partition. This is the preferred boot partition, as determined by the partition table & any OTA sequence number found in OTA data. This partition will only be booted if it contains a valid app image, otherwise load_boot_image() will search for a valid partition using this selection as the starting point.