ARM: dts: lpc32xx: phy3250: avoid extension of device nodes by absolute path

The change simplifies layout of PHY3250 board description by
referencing device nodes of LPC32xx controllers by label.

No functional change intended.

Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>