arm64: Fix MINSIGSTKSZ and SIGSTKSZ

MINSIGSTKSZ and SIGSTKSZ for ARM64 are not correctly set in latest kernel.
This patch fixes this issue.

This issue is reported in LTP (testcase: sigaltstack02.c).
Testcase failed when sigaltstack() called with stack size "MINSIGSTKSZ - 1"
Since in Glibc-2.22, MINSIGSTKSZ is set to 5120 but in kernel
it is set to 2048 so testcase gets failed.

Testcase Output:
sigaltstack02 1  TPASS  :  stgaltstack() fails, Invalid Flag value,errno:22
sigaltstack02 2  TFAIL  :  sigaltstack() returned 0, expected -1,errno:12

Reported Issue in Glibc Bugzilla:
Bugfix in Glibc-2.22: [Bug 16850]
https://sourceware.org/bugzilla/show_bug.cgi?id=16850

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Akhilesh Kumar <akhilesh.k@samsung.com>
Signed-off-by: Manjeet Pawar <manjeet.p@samsung.com>
Signed-off-by: Rohit Thapliyal <r.thapliyal@samsung.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/uapi/asm/signal.h

@@ -19,6 +19,9 @@
 /* Required for AArch32 compatibility. */
 #define SA_RESTORER	0x04000000
 
+#define MINSIGSTKSZ 5120
+#define SIGSTKSZ    16384
+
 #include <asm-generic/signal.h>
 
 #endif

include/uapi/asm-generic/signal.h

@@ -80,8 +80,10 @@
  *	SA_RESTORER	0x04000000
  */
 
+#if !defined MINSIGSTKSZ || !defined SIGSTKSZ
 #define MINSIGSTKSZ	2048
 #define SIGSTKSZ	8192
+#endif
 
 #ifndef __ASSEMBLY__
 typedef struct {