cheza: Enable some button features
cheza: Enable some button features

Enable the following button features:
 * CONFIG_BUTTON_TRIGGERED_RECOVERY: Use volume buttons to trigger
   recovery mode during reboot.
 * CONFIG_EMULATED_SYSRQ: Send sysrq events when pressing some volume
   button sequences.
 * CONFIG_CMD_BUTTON: Console commands to emulate the volume buttons.

BRANCH=none
BUG=b:74395451
TEST=Holding power, volume_up, and volume_down buttons to reboot.
Checked the hostevent mask 0x4000 set.
TEST=Holding volume_up and volume_down to trigger debug mode.
Pressing some volume_up and volume_down sequences to send sysrq.
TEST=Typing "button vup" and "button vdown" console commands.

Change-Id: I7000012d85faf71a022cc8056bb7799c29f9d0bf
Signed-off-by: Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1200070
Reviewed-by: Alexandru M Stan <1784cbba6d7675b1eba55eaefe41c7672ad9da3b@chromium.org>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec