MIPS: vmlinux: discard .MIPS.abiflags

Discard .MIPS.abiflags from vmlinux. It's not needed and will cause
issues e.g. with old OCTEON bootloaders that cannot tolerate
additional program headers.

Before the patch:

$ readelf --program-headers octeon-vmlinux

Elf file type is EXEC (Executable file)
Entry point 0xffffffff815d09d0
There are 3 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  ABIFLAGS       0x00000000005e77f0 0xffffffff816e67f0 0xffffffff816e67f0
                 0x0000000000000018 0x0000000000000018  R      8
  LOAD           0x0000000000001000 0xffffffff81100000 0xffffffff81100000
                 0x0000000000b57f80 0x0000000001b86360  RWE    1000
  NOTE           0x00000000004e02e0 0xffffffff815df2e0 0xffffffff815df2e0
                 0x0000000000000024 0x0000000000000024  R      4

After the patch:

$ readelf --program-headers octeon-vmlinux

Elf file type is EXEC (Executable file)
Entry point 0xffffffff815d09d0
There are 2 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000001000 0xffffffff81100000 0xffffffff81100000
                 0x0000000000b57f80 0x0000000001b86360  RWE    1000
  NOTE           0x00000000004e02e0 0xffffffff815df2e0 0xffffffff815df2e0
                 0x0000000000000024 0x0000000000000024  R      4
Suggested-by: Matthew Fortune <matthew.fortune@imgtec.com>
Suggested-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: linux-mips@linux-mips.org
Cc: David Daney <ddaney.cavm@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/11402/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/vmlinux.lds.S

@@ -181,6 +181,7 @@ SECTIONS
 	DISCARDS
 	/DISCARD/ : {
 		/* ABI crap starts here */
+		*(.MIPS.abiflags)
 		*(.MIPS.options)
 		*(.options)
 		*(.pdr)