[bootloader] Report SMBIOS entry point to zircon

This adds a new bootdata type, BOOTDATA_SMBIOS, which provides the
address of the SMBIOS entry point table.

Change-Id: I59b6454b81146e822da6c6f084f6333880fab314

[bootloader] Fix logic in ACPI RSDP search

The comparison was always false. The code worked with the erroneous
comparison, since the following check made sure it found the correct
entry.

Change-Id: I64fc509d03455d0f83648bbeb39b6d8352d7c23d

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[bootloader] commandline processing overhaul

- maintain a single central commandline
- simplify interface to this commandline
- ensure that later additions to the commandline
correctly override same-named existing entries
- split legacy boot path into its own file
- bump bootloader version
- display bootloader version next to bootloader name
- disable some debug chatter, declutter things a bit

Change-Id: I86e10bddd156089582bcb079018e5bb780cbbf24