kernel/x86: merge "generic" into "legacy"

There is a desire to reduce the time spent on x86 OpenWRT platforms.
"generic" is most suitable for removal.  The few systems which could
use "generic" must now opt for "legacy" (or for a lucky few "64").

Closes: openwrt#14231
Signed-off-by: Elliott Mitchell <ehem+openwrt@m5p.com>

target/linux/x86/Makefile

@@ -8,7 +8,7 @@ ARCH:=i386
 BOARD:=x86
 BOARDNAME:=x86
 FEATURES:=squashfs ext4 vdi vmdk vhdx pcmcia targz fpu boot-part rootfs-part
-SUBTARGETS:=generic legacy geode 64
+SUBTARGETS:=legacy geode 64
 
 KERNEL_PATCHVER:=6.1
 KERNEL_TESTING_PATCHVER:=6.6