[BOARD] rely on manifest when copying *.conf files (#39)

workaround for genimage omitting hidden files when using `mountpoint` directive

board/miyoo/boot/configs/manifest

@@ -4,6 +4,8 @@
 !   to_file is optional; if missing will use from_file
 .backlight.conf
 .volume.conf
+.buttons.conf
+.batterylow.conf
 gmenu2x.conf gmenu2x/gmenu2x.conf
 input.conf gmenu2x/input.conf
 ! leave this last line here

board/miyoo/genimage-sdcard.cfg

@@ -20,6 +20,12 @@ image bootfs.vfat {
 		file configs/.volume.conf {
 			image = "boot/configs/.volume.conf"
 		}
+		file configs/.backlight.conf {
+			image = "boot/configs/.buttons.conf"
+		}
+		file configs/.backlight.conf {
+			image = "boot/configs/.batterylow.conf"
+		}
 		file configs/.backlight.conf {
 			image = "boot/configs/.backlight.conf"
 		}

board/miyoo/main/.backlight.conf

@@ -1 +0,0 @@
-9

board/miyoo/main/.volume.conf

@@ -1 +0,0 @@
-7