arm64: fix build for linux 4.4.21

linux 4.4.21 adds 2 new symbols for arm64.

Signed-off-by: Álvaro Fernández Rojas <[email protected]>

target/linux/arm64/config-4.4

@@ -81,7 +81,9 @@ CONFIG_BSD_PROCESS_ACCT=y
 CONFIG_BSD_PROCESS_ACCT_V3=y
 CONFIG_BUILD_BIN2C=y
 # CONFIG_CAVIUM_ERRATUM_22375 is not set
+# CONFIG_CAVIUM_ERRATUM_23144 is not set
 # CONFIG_CAVIUM_ERRATUM_23154 is not set
+# CONFIG_CAVIUM_ERRATUM_27456 is not set
 CONFIG_CC_OPTIMIZE_FOR_SIZE=y
 CONFIG_CLKDEV_LOOKUP=y
 CONFIG_CLKSRC_ACPI=y