x86/mm: Report actual image regions in /proc/iomem

The resource reservations in /proc/iomem made for the kernel image did
not reflect the gaps between text, rodata, and data. Add the "rodata"
resource and update the start/end calculations to match the respective
calls to free_kernel_image_pages().

Before (booted with "nokaslr" for easier comparison):

00100000-bffd9fff : System RAM
  01000000-01e011d0 : Kernel code
  01e011d1-025619bf : Kernel data
  02a95000-035fffff : Kernel bss

After:

00100000-bffd9fff : System RAM
  01000000-01e011d0 : Kernel code
  02000000-023d4fff : Kernel rodata
  02400000-025619ff : Kernel data
  02a95000-035fffff : Kernel bss

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-ia64@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Robert Richter <rrichter@marvell.com>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>
Cc: Will Deacon <will@kernel.org>
Cc: x86-ml <x86@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Link: https://lkml.kernel.org/r/20191029211351.13243-29-keescook@chromium.org