Add init.environ.rc to aosp_riscv64

init.environ.rc has a postinstall command to create the symlinks in
and directories in the root filesystem.  Without those packaging
target-files.zip fails with:
failed to find system in canned fs_config

Bug: 250918230
Test: lunch aosp_riscv64-userdebug && m installclean && m droid dist
Change-Id: Iccb6ba53a3caa918431119230256a01d4919f1cc

target/product/aosp_riscv64.mk

@@ -61,6 +61,7 @@ endif
 # TODO: this list should come via mainline_system.mk, but for now list
 # just the modules that work for riscv64.
 PRODUCT_PACKAGES := \
+  init.environ.rc \
   init_system \
   linker \
   shell_and_utilities \