Suggestions from delphij, thanks!

replace if chain by switch. Print out entire zap_block_type.

In D22139#496705, @greg_unrelenting.technology wrote:

Would it be possible to also support memory-mapped UART this way? Intel >=Skylake and all aarch64 systems use mmio.
I've added an SPCR table to my Kaby Lake laptop to configure the UART, but it would be nice if it could auto configure without SPCR.

Rename comconsole.c to efiserialio.c to avoid issues with libi386/comconsole.c.
On x86, use libi386/comconsole because we still can not ensure the proper order
of serial ports and there is known issue on some systems with input on serial.

really check the device node type. Free unused devpaths by calling
efi_close_devpath().

need to handle usb luns

left over debug printf.

Seems ok.
Note, the issue about the staging size is not really if we can or can not allocate specific size, but if we have enough target space to copy it. I have starting to port other change (https://reviews.freebsd.org/D22309), the idea there is that we should determine if the target location has enough space. The bios version is simple as there we own the memory and we can not load directly to target address, in UEFI case we need to allocate, load and after switching off the BS, only then we can copy.

Wrong place for efi_devpath_trim.
No need to walk partitions in efipart_find_parent.
No need for local variable.