loader.efi: efipart should be more careful about constructing block device lists

[tsoome]

Summary

The cd handles should be collected as list of partitions. Some systems also provide base name for block device (like PciRoot(0x0)/Pci(0x5,0x0)), we need to be careful about those.

To make out life a bit easier, we prepare not just an array of handles, but we allocate pdinfo struct for each handle and devicepath, then we can simplify our work to sort the devices.

Test Plan

Tested with vmware fusion and bhyve.

[tsoome]

review suggestions from illumos.