rtsm linux: add minimal linux configuration with submodule

Guest linux included submodule "linux-rtsm"
Add filesystem file "fs.cpio", device tree binary file "host-a15.dtb"
Add usage at README.md, how test linux guest on RTSM with bare-metal guest.


README.md
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Testing minimal linux on RTSM fastmodels using git submodule
Download linux-rtsm
$ git submodule init
$ git submodule update
Initial setup for linux
$ cd linux-rtsm
$ git checkout 7d1f9aeff1ee4a20b1aeb377dd0f579fe9647619 -b 3.8
$ git apply ../patch/linux-fastmodels-config-add-minimal-linux-config.patch
$ cp ../linuxguest/fs.cpio ./
$ cp ../linuxguest/host-a15.dtb ./
Building linux-arndale
$ make ARCH=arm vexpress_minhw_defconfig
$ CROSS_COMPILE=arm-linux-gnueabi- ARCH=arm make -j8
$ cat host-a15.dtb >> arch/arm/boot/zImage
Loading khypervisor to RTSM fastmodels
$ cp arch/arm/boot/zImage ../monitor/zImage
$ cd ../monitor
$ make LINUX=y
Run and Debug on DS-5 or FastModels MaxView + RTSM VE Cortex A15-A7
$ maxview &
Under monitor/ directory 
$ ./run_rtsm.sh
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