ARM: dts: lpc32xx: ea3250: add SoC name prefix to board dts file

To simplify matching of DTS files of all NXP LPC32xx powered boards by
a file name add 'lpc3250' prefix to Embedded Artists LPC3250 board dts
file.

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