powerpc/64: Fix unannotated intra-function call warning

objtool throws the following warning:
  arch/powerpc/kernel/head_64.o: warning: objtool: .text+0x6128:
  unannotated intra-function call

Fix the warning by annotating start_initialization_book3s symbol with the
SYM_FUNC_START_LOCAL and SYM_FUNC_END macros.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Fixes: 58f24eea ("powerpc/64s: Refactor initialisation after prom")
Suggested-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230217043226.1020041-1-sv@linux.ibm.com