Build: Rename TFM_PLATFORM

Arm platforms are moved into arm folder, so the build command
TFM_PLATFORM should do the corresponding changes.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: Iba23e4f71d5c5865f358c2b7ce612ba603eff4e7
diff --git a/script/tf-coverity/cov-makefile b/script/tf-coverity/cov-makefile
index 79f34ea..1ca296d 100644
--- a/script/tf-coverity/cov-makefile
+++ b/script/tf-coverity/cov-makefile
@@ -14,9 +14,9 @@
 BASE_DIR ?= .
 
 target_platforms := cypress/psoc64 \
-                    mps2/an519 mps2/an521 \
-                    mps3/an524 \
-                    musca_b1/sse_200 musca_s1
+                    arm/mps2/an519 arm/mps2/an521 \
+                    arm/mps3/an524 \
+                    arm/musca_b1/sse_200 arm/musca_s1
 
 tf_m := trusted-firmware-m