dts: arm: npcx: refactor the RAM configuration

The last 2k bytes of the data RAM is used by the booter in some npcx EC
chips. This commit adds a bootloader_ram DT node to describe this
additional layout of the RAM. As a result, we can determine the total
RAM size by adding the size of flash0, sram0, and bootloader_ram.

Also, this commit moves 64k bytes from the code RAM (flash0) to the data
RAM (sram0) for npcx7m7fc because its internal flash is 512K bytes.
(In the Chromebook application, we need the code RAM size <= half of the
flash size.)

Signed-off-by: Jun Lin <CHLin56@nuvoton.com>