ARM: dts: msm: Update memory map for msmtitanium

Memory map for msmtitanium has been updated, size
of external_mem region has been increased by 3MB
and start address of modem region has been shifted
by 4MB. Correspondingly update the memory map.

Change-Id: Ic7f9f040b5b050bfd1838818195c92fdbb361b17
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>