powerpc: Fix missing CRCs, add more asm-prototypes.h declarations

Add declarations for:
  - __mfdcr, __mtdcr (if CONFIG_PPC_DCR_NATIVE=y; through <asm/dcr.h>)
  - switch_mmu_context (if CONFIG_PPC_BOOK3S_64=n; through <asm/mmu_context.h>)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/asm-prototypes.h

@@ -17,6 +17,8 @@
 #include <asm/checksum.h>
 #include <linux/uaccess.h>
 #include <asm/epapr_hcalls.h>
+#include <asm/dcr.h>
+#include <asm/mmu_context.h>
 
 #include <uapi/asm/ucontext.h>