[PATCH] selftest/vm: Fix build error

[Xingxing Su <suxingxing@xxxxxxxxxxx>]

Only x86 and PowerPC implement the pkey-xxx.h, 
and an error was reported when compiling protection_keys.c.

Add a Arch judgment to compile "protection_keys" in the Makefile.

If other arch implement this, add the arch name to the Makefile.
eg:
    ifneq (,$(findstring $(ARCH),powerpc mips ... ))

Following build errors:
    pkey-helpers.h:93:2: error: #error Architecture not supported
     #error Architecture not supported
    pkey-helpers.h:96:20: error: ‘PKEY_DISABLE_ACCESS’ undeclared
     #define PKEY_MASK (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE)
                        ^
    protection_keys.c:218:45: error: ‘PKEY_DISABLE_WRITE’ undeclared
     pkey_assert(flags & (PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE));
                                                ^

Signed-off-by: Xingxing Su <suxingxing@xxxxxxxxxxx>
---
 tools/testing/selftests/vm/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
index 30873b1..691893a 100644
--- a/tools/testing/selftests/vm/Makefile
+++ b/tools/testing/selftests/vm/Makefile
@@ -60,9 +60,13 @@ ifeq ($(CAN_BUILD_X86_64),1)
 TEST_GEN_FILES += $(BINARIES_64)
 endif
 else
+
+ifneq (,$(findstring $(ARCH),powerpc))
 TEST_GEN_FILES += protection_keys
 endif
 
+endif
+
 ifneq (,$(filter $(MACHINE),arm64 ia64 mips64 parisc64 ppc64 ppc64le riscv64 s390x sh64 sparc64 x86_64))
 TEST_GEN_FILES += va_128TBswitch
 TEST_GEN_FILES += virtual_address_range
-- 
1.8.3.1