Integrate with FireMarshal (w/ Chipyard) (keystone-enclave#208)

Keystone software stack has been integrated with FireMarshal
which is a software management tool for FireSim in Chipyard (https://chipyard.readthedocs.io/)
Now Keystone can be built with FireMarshal using the following workload config:
https://github.com/keystone-enclave/firemarshal-keystone

* Add target "patch" for applying patches without building
* Bump Linux 5.6
* Bump Linux driver (includes compatibility fixes for 5.6)
* Removed defconfig for FireSim because it's now in firemarshal-keystone workload config
* Update Documentation for FireSim

CMakeLists.txt

@@ -183,7 +183,6 @@ else()
   add_patch("linux" "linux${BITS}.patch" ${linux_srcdir} linux_patches)
 endif()
 
-
 if(initramfs)
   # linux-initramfs
   execute_process(COMMAND id -u OUTPUT_VARIABLE uid)
@@ -290,6 +289,10 @@ add_custom_target("image" DEPENDS "buildroot" "sm"
 )
 add_dependencies("buildroot" "image-deps")
 
+###############################################################################
+## PATCH
+###############################################################################
+add_custom_target("patch" DEPENDS ${qemu_patches} ${linux_patches} ${sm_patches})
 
 ###############################################################################
 ## QEMU scripts