ar7: refresh kernel configuration

The configuration of the generic subtarget was used as the default
configuration and then the subtarget configurations were adapted.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/ar7/config-4.9

@@ -18,6 +18,8 @@ CONFIG_ARCH_SUSPEND_POSSIBLE=y
 CONFIG_ARCH_USE_BUILTIN_BSWAP=y
 CONFIG_ARCH_WANT_IPC_PARSE_VERSION=y
 CONFIG_BOOT_ELF32=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y
+# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
 CONFIG_CEVT_R4K=y
 CONFIG_CLONE_BACKWARDS=y
 CONFIG_CMDLINE="rootfstype=squashfs,jffs2"
@@ -105,6 +107,7 @@ CONFIG_KALLSYMS=y
 CONFIG_LEDS_GPIO=y
 CONFIG_LEDS_TRIGGER_HEARTBEAT=y
 CONFIG_MDIO_BOARDINFO=y
+CONFIG_MIGRATION=y
 CONFIG_MIPS=y
 CONFIG_MIPS_ASID_BITS=8
 CONFIG_MIPS_ASID_SHIFT=0