[source] build: fix aarch64 default cpu selection

[LEDE Commits]

yousong pushed a commit to source.git, branch master:
https://git.lede-project.org/b889d1e3cf0233e6efbf4b55197ab64aa8c0cd6a

commit b889d1e3cf0233e6efbf4b55197ab64aa8c0cd6a
Author: Yousong Zhou <yszhou4tech at gmail.com>
AuthorDate: Wed Apr 19 17:34:18 2017 +0800

    build: fix aarch64 default cpu selection
    
    Not sure since when the issue emerged, but according to the current doc of gcc
    and as, armv8-a is intended as argument of -march
    
    The change will affect at the moment arm64 and layerscape/64b
    
    Below is the relevant error messages when building toolchain
    
        Assembler messages:
        Error: unknown cpu `armv8-a'
        Error: unrecognized option -mcpu=armv8-a
        /home/yousong/git-repo/lede-project/lede/build_dir/toolchain-aarch64_armv8-a_gcc-5.4.0_musl/gcc-5.4.0/libgcc/libgcc2.c:1:0: error: unknown value 'armv8-a' for -mcpu
    
    Signed-off-by: Yousong Zhou <yszhou4tech at gmail.com>
---
 include/target.mk | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/target.mk b/include/target.mk
index 3523d04..646057c 100644
--- a/include/target.mk
+++ b/include/target.mk
@@ -208,8 +208,8 @@ ifeq ($(DUMP),1)
     CPU_CFLAGS_ultrasparc = -mcpu=ultrasparc
   endif
   ifeq ($(ARCH),aarch64)
-    CPU_TYPE ?= armv8-a
-    CPU_CFLAGS_armv8-a = -mcpu=armv8-a
+    CPU_TYPE ?= generic
+    CPU_CFLAGS_generic = -mcpu=generic
     CPU_CFLAGS_cortex-a53 = -mcpu=cortex-a53
   endif
   ifeq ($(ARCH),arc)