arch/x86/include/asm/efi.h: fix build failure

arch/x86/include/asm/efi.h: fix build failure

With KMEMCHECK=y, KASAN=n:

  arch/x86/platform/efi/efi.c:673:3: error: implicit declaration of function `memcpy' [-Werror=implicit-function-declaration]
  arch/x86/platform/efi/efi_64.c:139:2: error: implicit declaration of function `memcpy' [-Werror=implicit-function-declaration]
  arch/x86/include/asm/desc.h:121:2: error: implicit declaration of function `memcpy' [-Werror=implicit-function-declaration]

Don't #undef memcpy if KASAN=n.

Fixes: 769a8089c1fd ("x86, efi, kasan: #undef memset/memcpy/memmove per arch")
Signed-off-by: Andrey Ryabinin <[email protected]>
Reported-by: Ingo Molnar <[email protected]>
Reported-by: Sedat Dilek <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>