binutils/objdump: Fix disassemble for huge elf sections

When elf section size is beyond unsigned int max value, objdump fails
to disassemble from that section. Ex on PowerPC,

  $ objdump -h /proc/kcore
    Idx  Name   Size       VMA
      4  load2  100000000  c000000000000000

Here, size of load2 section is 0x100000000. Also note that, 0xc00....
address range is kernel space for PowerPC. Now let's try to disassemble
do_sys_open() using /proc/kcore.

  $ cat /proc/kallsyms | grep -A1 -w do_sys_open
    c00000000036c000 T do_sys_open
    c00000000036c2d0 T SyS_open

Before patch:

  $ objdump -d --start-address=0xc00000000036c000 --stop-address=0xc00000000036c2d0 /proc/kcore
    /proc/kcore:    file format elf64-powerpcle

    Disassembly of section load2:

    c00000000036c000 <load2+0x36c000>:
    c00000000036c000:    Address 0xc00000000036c000 is out of bounds.

Fix this by changing type of 'buffer_length' from unsigned int to
size_t. After patch:

  $ objdump -d --start-address=0xc00000000036c000 --stop-address=0xc00000000036c2d0 /proc/kcore
    /proc/kcore:    file format elf64-powerpcle

    Disassembly of section load2:

    c00000000036c000 <load2+0x36c000>:
    c00000000036c000: fc 00 4c 3c     addis   r2,r12,252
    c00000000036c004: 00 53 42 38     addi    r2,r2,21248
    c00000000036c008: a6 02 08 7c     mflr    r0

include/
	* dis-asm.h (struct disassemble_info): Change type of buffer_length
	field to size_t.
opcodes/
	* dis-buf.c (buffer_read_memory): Change type of end_addr_offset,
	max_addr_offset and octets variables to size_t.

include/dis-asm.h

@@ -158,7 +158,7 @@ typedef struct disassemble_info
   /* These are for buffer_read_memory.  */
   bfd_byte *buffer;
   bfd_vma buffer_vma;
-  unsigned int buffer_length;
+  size_t buffer_length;
 
   /* This variable may be set by the instruction decoder.  It suggests
       the number of bytes objdump should display on a single line.  If