[virtcon] Don't update framebuffer with no display

This change reduces how much work the virtcon does when it doesn't have
ownership of the display. First, add checks for ownership to all checks
for the presence of a display (i.e. vc_gfx being non-null), so we treat
not having ownership the same as not having a framebuffer to render to.
Second, add ownership checks to all checks for vc->active, so we treat
not having ownership as all virtcons being inactive.

Test: Check that output during no display appears when focus is gained
Change-Id: Ib8ca77b0c9a104131bd37756878b30f7136c1b38

[virtcon] Define missing symbols needed by vc-input.cpp

vc-input.cpp depends on vc_toggle_framebuffer and g_vc_owns_display that
are defined by vc-display.cpp. However, vc-display.cpp is not being
included when building virtual-console-test. This wasn't an issue in the
past because --gc-sections would discard all functions that invoke these
symbols, but this breaks with profiling which is incompatible with
--gc-sections.

Test: manually
Change-Id: Ia6ab73b3599d996957ae3eb63f11e788ca96bbfb

[virtcon] Add support for hotplugging

This change adds support for hotplugging to the virtcon. If multiple
displays are connected, the virtcon will use the display which was
attached first. The virtcon's contents and scrollback are kept when
switching between displays, although long lines will be truncated if
the virtcon moves to a smaller display.

When no display is connected, the console continues to function
normally, except without rendering anything. All checks for whether or
not any gfx operations should be done are in vc-device.

Change-Id: I467b9b1792f4d43803b521ec564dfe1873b85a97

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[zircon][mxtl->fbl] Rename mxtl to fbl

Change-Id: Ie21b6498e1bfb0a7fa0315e40b9e5c3ee78646be

[devmgr][virtcon] display netsvc output on vc1 in netboot mode

- virtcon can now execute a specific command in vc1 if one is
provided via the --run option
- virtcon uses a white-on-blue color scheme for this
- devmgr provides --run dlog ... when starting netsvc in netboot
mode

Change-Id: I7008db178aa25a8f3dc549a7af46d790d11c6472

[virtcon] Use the new MX_OK and MX_ERR_* mx_status_t names

Change-Id: I89dd39bd11d4d4b89321424cfc910b605688e307

[virtcon] cleanup

- remove some unused header includes
- remove unused vcdebug.h (xprintf was not used and now virtcon
filters its own debug prints out of the debug log console so
printf is safe to use if needed)
- clean up rules.mk to better reflect shared sources, libraries
- move shared code from main.cpp to vc-input.cpp
- no longer include main.cpp in virtual-console-test
- remove global lock, no longer needed in new single threaded design

Change-Id: I5aacc0f95f817f25ce96bbfa2f74d4877e9c4a16

[gfxconsole][virtcon] move and rename gfxconsole to virtcon

It's no longer a device, it's time for it to leave the
land of devices.

Change-Id: I977c56dbacb0794e6f67daac1dd6e3f4f2632f3d