lib: uuid: add functions to generate UUID version 4

This patch adds support to generate UUID (Universally Unique Identifier)
in version 4 based on RFC4122, which is randomly.

Source: https://www.ietf.org/rfc/rfc4122.txt

Changes:
- new configs:
  - CONFIG_LIB_UUID for compile lib/uuid.c
  - CONFIG_RANDOM_UUID for functions gen_rand_uuid() and gen_rand_uuid_str()
- add configs dependency to include/config_fallbacks.h for lib uuid.

lib/uuid.c:
- add gen_rand_uuid() - this function writes 16 bytes len binary representation
  of UUID v4 to the memory at given address.

- add gen_rand_uuid_str() - this function writes 37 bytes len hexadecimal
  ASCII string representation of UUID v4 to the memory at given address.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
[trini: Add CONFIG_EFI_PARTITION to fallbacks]
Signed-off-by: Tom Rini <trini@ti.com>

include/config_fallbacks.h

@@ -55,6 +55,20 @@
 #define HAVE_BLOCK_DEVICE
 #endif
 
+#if (defined(CONFIG_PARTITION_UUIDS) || \
+	defined(CONFIG_EFI_PARTITION) || \
+	defined(CONFIG_RANDOM_UUID) || \
+	defined(CONFIG_BOOTP_PXE)) && \
+	!defined(CONFIG_LIB_UUID)
+#define CONFIG_LIB_UUID
+#endif
+
+#if defined(CONFIG_RANDOM_UUID) && \
+	!defined(CONFIG_LIB_RAND) && \
+	!defined(CONFIG_LIB_HW_RAND)
+#define CONFIG_LIB_RAND
+#endif
+
 #ifndef CONFIG_SYS_PROMPT
 #define CONFIG_SYS_PROMPT	"=> "
 #endif