Add send_hardware_nmi to Grapefruit

[mkeeter]

This is another small improvement for #1983

It needs testing on actual hardware!

[citrus-it]

standish% h hiffy -c Sequencer.send_hardware_nmi
humility: attached to 0483:3754:0040003A3431511837393330 via ST-Link V3
Sequencer.send_hardware_nmi() => Err(<server died; its new ID is 0>)

ID TASK                       GEN PRI STATE
12 grapefruit_seq               0   4 FAULT: mem fault (precise: 0x60000308) in task code (was: ready)

See /staff/andy/hubris.core.grapefruit_seq.0

[citrus-it]

Tested on sapphire:

standish% h hiffy -c Sequencer.send_hardware_nmi
humility: attached to 0483:3754:0040003A3431511837393330 via ST-Link V3
Sequencer.send_hardware_nmi() => ()

Meanwhile, back at the ranch:

teapot console login:

NMI received: entering kmdb


Welcome to kmdb
Loaded modules: [ ipcc unix krtld apix genunix specfs mm ]
[0]>