common/cmd_bootm: extend do_bootm_vxworks to support the new VxWorks boot interface.

The next version VxWorks adopts device tree (for PowerPC and ARM) as its hardware
description mechanism. For PowerPC, the boot interface conforms to
the ePAPR standard, which is:

   void (*kernel_entry)(ulong fdt_addr,
          ulong r4 /* 0 */,
          ulong r5 /* 0 */,
          ulong r6 /* EPAPR_MAGIC */, ulong r7 /* IMA size */,
          ulong r8 /* 0 */, ulong r9 /* 0 */)

For ARM, the boot interface is:

   void (*kernel_entry)(void *fdt_addr)

Signed-off-by: Miao Yan <miao.yan@windriver.com>
[trini: Fix build error when !CONFIG_OF_FDT is set, typo on PowerPC,
missing extern ft_fixup_num_cores]
Signed-off-by: Tom Rini <trini@ti.com>