Add sys.slpi.firmware.version property.

Bug: 38240024
Test: Verified value of sys.spli.firmware.version property.  See details in
testing done comment in
https://googleplex-android-review.git.corp.google.com/2442584 .
Change-Id: Ief04cbfac4efd71c8ff22057fc286645fbadf44d

init.qcom.devstart.sh

@@ -3,3 +3,8 @@
 echo 1 > /sys/kernel/boot_adsp/boot
 echo 1 > /sys/kernel/boot_slpi/boot
 setprop sys.qcom.devup 1
+
+version=`grep -ao "OEM_IMAGE_VERSION_STRING[ -~]*" \
+              /vendor/firmware/slpi_v2.b04 | \
+         sed -e s/OEM_IMAGE_VERSION_STRING=SLPI.version.// -e s/\(.*\).//`
+setprop sys.slpi.firmware.version "$version"

sepolicy/vendor/init-devstart-sh.te

@@ -6,6 +6,9 @@ init_daemon_domain(init-qcom-devstart-sh)
 allow init-qcom-devstart-sh vendor_shell_exec:file rx_file_perms;
 allow init-qcom-devstart-sh vendor_toolbox_exec:file rx_file_perms;
 
+# execute grep
+allow init-qcom-devstart-sh vendor_file:file rx_file_perms;
+
 # Set the sys.qcom.devup property
 set_prop(init-qcom-devstart-sh, system_prop)