Add action for RISC-V CI workflow (#334)

* Fixes for RISCV build

* Consolidate compiler flags

* Added RISC-V continuous integration script

* Added workflow for RISC-V CI action
Co-authored-by: NAdvait Jain <advaitjain@users.noreply.github.com>

.github/workflows/riscv.yml

+
+name: RISC-V
+
+# https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#onschedule
+on:
+  schedule:
+    # 10am UTC is 3am or 4am PT depending on daylight savings.
+    - cron: '0 10 * * *'
+
+  # Allow manually triggering of the workflow.
+  workflow_dispatch: {}
+
+jobs:
+  riscv_daily:
+    runs-on: ubuntu-latest
+
+    if: |
+      github.event_name == 'workflow_dispatch' ||
+      (github.event_name == 'schedule' && github.repository == 'tensorflow/tflite-micro')
+
+    name: RISC-V Continuous Builds
+    steps:
+      - uses: actions/checkout@v2
+      - name: Test
+        run: |
+          tensorflow/lite/micro/tools/ci_build/test_riscv.sh