perf bench: Update the copies of x86's mem{cpy,set}_64.S

And update linux/linkage.h, which requires in turn that we make these
files switch from ENTRY()/ENDPROC() to SYM_FUNC_START()/SYM_FUNC_END():

  tools/perf/arch/arm64/tests/regs_load.S
  tools/perf/arch/arm/tests/regs_load.S
  tools/perf/arch/powerpc/tests/regs_load.S
  tools/perf/arch/x86/tests/regs_load.S

We also need to switch SYM_FUNC_START_LOCAL() to SYM_FUNC_START() for
the functions used directly by 'perf bench', and update
tools/perf/check_headers.sh to ignore those changes when checking if the
kernel original files drifted from the copies we carry.

This is to get the changes from:

  6dcc5627 ("x86/asm: Change all ENTRY+ENDPROC to SYM_FUNC_*")
  ef1e0315 ("x86/asm: Make some functions local")
  e9b9d020 ("x86/asm: Annotate aliases")

And address these tools/perf build warnings:

  Warning: Kernel ABI header at 'tools/arch/x86/lib/memcpy_64.S' differs from latest version at 'arch/x86/lib/memcpy_64.S'
  diff -u tools/arch/x86/li...