ARM: rmobile: salvator-x: Zap redefined DECLARE_GLOBAL_DATA_PTR

The macro is used twice in the salvator-x board file, drop one.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>