meowth_fp: enable STOP mode
meowth_fp: enable STOP mode

use CONFIG_LOW_POWER_IDLE to put the STM32H7 in low-power mode when
possible.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=poppy
BUG=b:75105319
TEST=On ZerbleBarn, use on-board INAs to measure idle power consumption,
 w/o  CONFIG_LOW_POWER_IDLE pp3300_h7_ma:14.0
 with CONFIG_LOW_POWER_IDLE pp3300_h7_ma:1.84
TEST=On Meowth, ran for 18h with this firmware, no hiccups, fingerprint
features still work, the MCU spent 18h - 64s in deep-sleep.

Change-Id: I7d656db1546a41547e8199e45b37c341ebf0e4b1
Reviewed-on: https://chromium-review.googlesource.com/1096768
Commit-Ready: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

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