Kobo: On sunxi, add a delay between the white flash and the sleep

screen.

Otherwise, on the Sage, weird flash glitches may happen, depending on
what was on screen...
(e.g., there's some weird update merging shenanigans going on
despite those updates being flagged NO_MERGE...).

frontend/device/generic/device.lua

@@ -9,7 +9,8 @@ local Geom = require("ui/geometry")
 local logger = require("logger")
 local util = require("util")
 local _ = require("gettext")
-local T = require("ffi/util").template
+local ffiUtil = require("ffi/util")
+local T = ffiUtil.template
 
 local function yes() return true end
 local function no() return false end
@@ -307,6 +308,11 @@ function Device:onPowerEvent(ev)
                     self.screen:clear()
                 end
                 self.screen:refreshFull()
+
+                -- On Kobo, on sunxi SoCs with a recent kernel, wait a tiny bit more to avoid weird refresh glitches...
+                if self:isKobo() and self:isSunxi() then
+                    ffiUtil.usleep(150 * 1000)
+                end
             end
         else
             -- nil it, in case user switched ScreenSaver modes during our lifetime.