tf-m-build-config: Update TARGET_PLATFORM and PROJ_CONFIG params

Rename TARGET_PLATFORM -> TFM_PLATFORM, remove unused PROJ_CONFIG. These
changes were done long ago on the tf-m-scripts side:
https://git.trustedfirmware.org/ci/tf-m-ci-scripts.git/commit/?id=b708f576db8dedaa1286d4bb23956b390f6a8a8a
, but never were propagated to Jenkins job params. This disallows to
rebuild an existing tf-m-build-config build or start one from scratch.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Idd13f50989df1ba75cda7092de94af742470a6f9
diff --git a/tf-m-build-config.yaml b/tf-m-build-config.yaml
index 56baba9..1ba2515 100644
--- a/tf-m-build-config.yaml
+++ b/tf-m-build-config.yaml
@@ -20,18 +20,12 @@
       - string:
           name: 'CONFIG_NAME'
       - string:
-          name: 'TARGET_PLATFORM'
+          name: 'TFM_PLATFORM'
           description: |
             Specifies the target platform.
             For more information see <a href="https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/plain/docs/getting_started/tfm_build_instruction.rst">here</a>.
           default: ''
       - string:
-          name: 'PROJ_CONFIG'
-          description: |
-            Specifies the way the application is built.
-            For more information see <a href="https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/plain/docs/getting_started/tfm_build_instruction.rst">here</a>.
-          default: ''
-      - string:
           name: 'COMPILER'
           description: |
             Specifies the compiler toolchain.