package/rpi-firmware: bump for enhancements and bug fixes

Fixes and enhancements for:
  - video: add 3D stereo, unusual streams with skipped frames
  - audio: reset-on-flush, alsa passthrough, volume
  - misc : SDRAM drive strength
  - some undocumented changes

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/rpi-firmware/rpi-firmware.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-RPI_FIRMWARE_VERSION = 04ba1c03780ae708c9289bce14f56933e55e9c20
+RPI_FIRMWARE_VERSION = 81e54c47b1cb26dd3990cbc970f4ddd3614196e8
 RPI_FIRMWARE_SITE = $(call github,raspberrypi,firmware,$(RPI_FIRMWARE_VERSION))
 RPI_FIRMWARE_LICENSE = BSD-3c
 RPI_FIRMWARE_LICENSE_FILES = boot/LICENCE.broadcom