Refactor programs/Makefile

This commit refactors the Makefile in the programs directory to remove
unused variables and consistent naming schemes.

Signed-off-by: Harry Ramsey <harry.ramsey@arm.com>
diff --git a/programs/Makefile b/programs/Makefile
index 7a390a4..b48a006 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -1,5 +1,4 @@
-TF-PSA-CRYPTO_PATH = ../tf-psa-crypto/
-TF-PSA-CRYPTO_PROGRAM_PATH = ../tf-psa-crypto/programs
+TF-PSA-CRYPTO_CORE_PATH = ../tf-psa-crypto/programs
 MBEDTLS_TEST_PATH = ../tests
 include ../scripts/common.make