mediatek: fix target FPU settings

This reverts commit 5555545494.
The target supports both NEON and VFPv4, but for this to work properly,
a few more changes are needed:
- enable NEON support in the kernel config
- add the fpu feature flag to the makefile

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/mediatek/32/target.mk

@@ -5,6 +5,7 @@
 SUBTARGET:=32
 BOARDNAME:=32bit
 CPU_TYPE:=cortex-a7
+CPU_SUBTYPE:=neon-vfpv4
 
 define Target/Description
 	Build firmware images for MediaTek 32bit ARM based boards.

target/linux/mediatek/Makefile

@@ -6,7 +6,7 @@ ARCH:=arm
 BOARD:=mediatek
 BOARDNAME:=MediaTek Ralink ARM
 SUBTARGETS:=32
-FEATURES:=squashfs nand ubifs
+FEATURES:=squashfs nand ubifs fpu
 MAINTAINER:=John Crispin <john@phrozen.org>
 
 KERNEL_PATCHVER:=4.14

target/linux/mediatek/config-4.14

@@ -334,7 +334,7 @@ CONFIG_MTK_TIMER=y
 CONFIG_MULTI_IRQ_HANDLER=y
 CONFIG_MUTEX_SPIN_ON_OWNER=y
 CONFIG_NEED_DMA_MAP_STATE=y
-# CONFIG_NEON is not set
+CONFIG_NEON=y
 CONFIG_NET_DSA=y
 CONFIG_NET_DSA_MT7530=y
 CONFIG_NET_DSA_TAG_MTK=y