boot: zephyr: auto-enable TEST_RANDOM_GENERATOR

When enabling `PSA_CRYPTO` and there is no entropy driver in the system.

This is needed because in that scenario `MBEDTLS_PSA_CRYPTO_LEGACY_RNG`
gets picked by the build system and it would previously automatically
`select TEST_RANDOM_GENERATOR` but this bit has been removed so it
now needs to be explicitly enabled.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>

Author: tomi-font

boot/zephyr/Kconfig

@@ -281,6 +281,7 @@ config BOOT_RSA_TF_PSA_CRYPTO_LEGACY
 	bool "Use legacy crypto from TF-PSA-Crypto (i.e. Mbed TLS 4.x)"
 	select BOOT_USE_MBEDTLS
 	select PSA_CRYPTO
+	select TEST_RANDOM_GENERATOR if !ENTROPY_HAS_DRIVER
 	select PSA_WANT_KEY_TYPE_RSA_PUBLIC_KEY
 	select PSA_WANT_ALG_RSA_PKCKS1_V15
 	select PSA_WANT_ALG_RSA_PSS
@@ -291,6 +292,7 @@ config BOOT_RSA_PSA
 	bool "Use PSA API crypto"
 	select BOOT_USE_PSA_CRYPTO
 	select PSA_CRYPTO
+	select TEST_RANDOM_GENERATOR if !ENTROPY_HAS_DRIVER
 	select MBEDTLS_ENABLE_HEAP if MBEDTLS_BUILTIN
 	select PSA_WANT_KEY_TYPE_RSA_PUBLIC_KEY
 	select PSA_WANT_ALG_RSA_PKCKS1_V15