ARM: dts: lpc32xx: add device node for IRAM on-chip memory

The change adds a new device node with description of generic SRAM
on-chip memory found on NXP LPC32xx SoC series and connected to AHB
matrix slave port 3.

Note that NXP LPC3220 SoC has 128KiB of SRAM memory, the other
LPC3230, LPC3240 and LPC3250 SoCs all have 256KiB SRAM space,
in the shared DTSI file this change specifies 128KiB SRAM size.

Also it's worth to mention that the SRAM area contains of 64KiB banks,
2 banks on LPC3220 and 4 banks on the other SoCs from the series, and
all SRAM banks but the first one have independent power controls,
the description of this feature will be added with the introduction of
power domains for the SoC series.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Cc: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Olof Johansson <olof@lixom.net>