efiboot changes for device tree overlays

[Jason Thorpe <thorpej%me.com@localhost>]

Folks...

I just checked in some changes that allow efiboot to load a configuration file (default: /etc/efiboot.plist) and apply device tree overlays specified in that file:

boot: loading /etc/efiboot.plist done.


>> NetBSD/evbarm EFI Boot (aarch64), Revision 1.9 (Sun Apr 21 21:30:04 UTC 2019) (from NetBSD 8.99.37)
Press return to boot now, any other key for boot prompt
booting netbsd - starting in 0 seconds.     
5987152+2630336+1951692+1824188 [689088+481308]=0xeb8298
boot: loading /stand/evbarm/dtb/sunxi-h3-h5-orangepi-zero-nas.dtbo done.
EHCI failed to shut down host controller.
EHCI failed to shut down host controller.
ok
[   1.0000000] uboot: args 0x58400000, 0, 0, 0
[   1.0000000] NetBSD/evbarm (fdt) booting ...
.
.
.


For the boot above, here is what my /etc/efiboot.plist file looks like:

<plist>
<dict>
        <key>device-tree-overlays</key>
        <array>
                <string>/stand/evbarm/dtb/sunxi-h3-h5-orangepi-zero-nas.dtbo</string>
        </array>
</dict>
</plist>


These changes can also pre-load the EFI environment variables from the plist.

Eventually, I plan to:

-- Write an efiboot man page that documents this stuff.

-- Add support for inlining DT overlays in the plist itself (as <data> objects).

-- Add support for other DT fixups (analogous to how the RPI loader can allow overlays to have parameters).

Please let me know if you have any questions or problems with the changes.

-- thorpej