linux: Add LTS version 5.10.81

Since Linux 5.10.80 upstream commit 403475be6d (drm/amdgpu/gmc6: fix DMA
mask from 44 to 40 bits) is included in the 5.10 stable series, which
fixes an issues with our Dell OptiPlex 5055 systems with an affected card:

    05:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Oland [Radeon HD 8570 / R7 240/340 OEM] [1002:6611] (rev 87)

linux-5.10.73-405.bee → linux-5.10.81-412.bee

@@ -13,7 +13,7 @@ KERNELVERSION=${KERNELVERSION}${PKGEXTRAVERSION_DASH}
 echo $KERNELVERSION
 
 # "https://cdn.kernel.org/pub/linux/kernel/v${PKGVERSION[1]}.x/linux-${PKGVERSION}${PKGEXTRAVERSION_DASH}.tar.xz"
-SRCURL[0]="https://beehive.molgen.mpg.de/40ec9411f1bb6909ab2dccd55a479143/linux-5.10.70.tar.xz"
+SRCURL[0]="https://beehive.molgen.mpg.de/328795c34500b338397440cf3d378e4f/linux-5.10.81.tar.xz"
 if [ -z "${PKGEXTRAVERSION_DASH}" ]; then
     SRCURL[0]="https://cdn.kernel.org/pub/linux/kernel/v${PKGVERSION[1]}.x/linux-${PKGVERSION}.tar.xz"
 else