Limit BPi M2+ boot cpufreq to 816MHz again

Due to overheating issues we chose to limit this board to 816MHz max based on cpuburn tests in the past. Setting got lost and is now applied again.

patch/u-boot/u-boot-sunxi/add-bpi-m2plus.patch

@@ -3,7 +3,7 @@ new file mode 100644
 index 0000000..e9a7ada
 --- /dev/null
 +++ b/configs/Sinovoip_BPI_M2_plus_defconfig
-@@ -0,0 +1,15 @@
+@@ -0,0 +1,16 @@
 +CONFIG_ARM=y
 +CONFIG_ARCH_SUNXI=y
 +CONFIG_MACH_SUN8I_H3=y
@@ -18,4 +18,5 @@ index 0000000..e9a7ada
 +# CONFIG_CMD_FPGA is not set
 +CONFIG_SUN8I_EMAC=y
 +CONFIG_USB_EHCI_HCD=y
++CONFIG_SYS_CLK_FREQ=816000000
 +CONFIG_MMC_SUNXI_SLOT_EXTRA=2