Add build-time option to boot0sio to reset terminal

[lev]

Summary

Some hardware/firmware leaves serial console in bogus state before calling user boot code. After that output of boot0sio could not be seen by user, which is inconvenient.
This diff adds compile-time option BOOT_BOOT0_RESET_TERM, which force boot0sio to send default VT-100 reset command <ESC>c before all output.
This option is not compatible with PXE and VOLUME_SERIAL options, due to space constrains. Only two of these three options could be selected together.
This option is turned off by default.

[imp]

stand/i386/boot0sio/Makefile

10

We're trying to migrate to -DWITH_BOOT0_RESET_TERM style, so please use that here if you can by adding that variable in src.conf, etc.

[imp]

stand/i386/boot0sio/Makefile

10

No. Like this

.include <src.opts.mk>

.if ${MK_BOOT0_RESET_TERM} != "no"
...
.endif

[lev]

Mea culpa.

[freqlabs]

tools/build/options/WITH_BOOT0_RESET_TERM

6

constraints.

[rpokala]

stand/i386/boot0/Makefile

17

send terminal reset command when, under what conditions?

I see the addition which feeds into src.conf.5, but does this need to be mentioned elsewhere, such as boot.8 or boot0cfg.8?

tools/build/options/WITH_BOOT0_RESET_TERM

4

before all output can be read two different ways:

1. before the first output
2. before each individual output

Please clarify.

[lev]

stand/i386/boot0/Makefile

17

Other boot0[sio] options are not described in boot.8 or boot0cfg.8, so I haven't add new option there.

[freqlabs]

Thank you!

[freqlabs]

stand/i386/boot0/boot0.S

597

s/teminal/terminal/

[rpokala]

LGTM, but I defer to @imp. Oh, and @kevans did a lot of stuff related to loader output as part of LuaLoader, so you might want to get his feedback as well.

[lev]

"Rebase" to latest head, solve conflicts.

[imp]

I think this is good. There's many other strings we might consider for the reset, but this is good.

[lev]

Regenerate against fresh git repository.