powerpc: move ASM_CONST and stringify_in_c() into asm-const.h

This patch moves ASM_CONST() and stringify_in_c() into
dedicated asm-const.h, then cleans all related inclusions.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: asm-compat.h should include asm-const.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/nohash/64/pgtable.h

@@ -8,6 +8,7 @@
 
 #include <asm/nohash/64/pgtable-4k.h>
 #include <asm/barrier.h>
+#include <asm/asm-const.h>
 
 #ifdef CONFIG_PPC_64K_PAGES
 #error "Page size not supported"