powerpc: Remove duplicate/unnecessary ifdefs

powerpc: Remove duplicate/unnecessary ifdefs

When an ifdef is used in the below manner, second one could be considered
as duplicate.

  ifdef DEFINE_A
  ...code block...
  ifdef DEFINE_A       <-- This is a duplicate.
  ...code block...
  endif
  else
  ifndef DEFINE_A     <-- This is also duplicate.
  ...code block...
  endif
  endif

More details about the script and methods used to find these code
patterns are in cover letter of [1].

Few places in arch/powerpc where this pattern was seen:

  paca.h:
  Hunk1: Code is under check of CONFIG_PPC64 from line 13, hence the
  second CONFIG_PPC64 at line 166 is a duplicate.
  Hunk2: CONFIG_PPC_BOOK3S_64 was defined back to back. Merged the two
  ifdefs.

  asm-offsets.c:
  Code is under check of CONFIG_PPC64 from line 176 hence second
  CONFIG_PPC64 at line 249 is a duplicate.

  powermac/feature.c:
  #ifndef CONFIG_PPC64 is used at line 2066. And then in #else again
  #ifdef CONFIG_PPC64 is used. Which is a duplicate since in #else means
  CONFIG_PPC64 is defined.

  xmon.c:
  Code is under the check of CONFIG_SMP from line 521 hence the same
  check of CONFIG_SMP at line 646 is a duplicate.

No functional change is intended here. It only aims to improve code
readability.

[1] https://lore.kernel.org/all/20240118080326.13137-1-sshegde@linux.ibm.com/

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240216053016.528906-1-sshegde@linux.ibm.com