ARM: zynq: reserve space for jump target in secondary trampoline

Add a zero argument to the .word directive in
zynq_secondary_trampoline.  Without an expression the assembler emits
nothing for the .word directive.

This makes it so that the intended range is communicated to ioremap
and outer_flush_range in zynq_cpun_start; e.g. for LE
trampoline_code_size evaluates to 12 now instead of 8.

Found by inspection.  I'm not aware of any real problem this fixes.
Tested by doing on online/offline loop on ZC702.

Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>