x86/boot/32: Extract efi_pe_entry() from startup_32()

The efi_pe_entry() body is somehow squashed into startup_32(). In the old days,
we forced startup_32() to start at offset 0x00 and efi_pe_entry() to start
at 0x10.

But this requirement was removed long time ago, in:

  99f857db

 ("x86, build: Dynamically find entry points in compressed startup code")

The way it is now makes the code less readable and illogical. Given
we can now safely extract the inlined efi_pe_entry() body from
startup_32() into a separate function, we do so and we separate it to two
functions as they are marked already: efi_pe_entry() + efi32_stub_entry().

We also annotate the functions appropriatelly by ENTRY+ENDPROC.

ABI offset is preserved:

  0000   128 FUNC    GLOBAL DEFAULT    6 startup_32
  0080    60 FUNC    GLOBAL DEFAULT    6 efi_pe_entry
  00bc    68 FUNC    GLOBAL DEFAULT    6 efi32_stub_entry

On the top-level, it looked like this:

	ENTRY(startup_32)
	#ifdef CONFIG_EFI_STUB		; start of inlined
		jmp     preferred_addr
	ENTRY(efi_pe_entry)
		... ; a lot of assembly (efi_pe_entry)
	ENTRY(efi32_stub_entry)
		... ; a lot of assembly (efi32_stub_entry)
		leal    preferred_addr(%eax), %eax
		jmp     *%eax
	preferred_addr:
	#endif				; end of inlined
		... ; a lot of assembly (startup_32)
	ENDPROC(startup_32)

And it is now converted into:

	ENTRY(startup_32)
		... ; a lot of assembly (startup_32)
	ENDPROC(startup_32)

	#ifdef CONFIG_EFI_STUB
	ENTRY(efi_pe_entry)
		... ; a lot of assembly (efi_pe_entry)
	ENDPROC(efi_pe_entry)

	ENTRY(efi32_stub_entry)
		... ; a lot of assembly (efi32_stub_entry)
		leal    startup_32(%eax), %eax
		jmp     *%eax
	ENDPROC(efi32_stub_entry)
	#endif

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: ard.biesheuvel@linaro.org
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20170824073327.4129-1-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>