Implement byte reading macros into library/

To improve readability by saving horizontal and vertical space.
Removed unecessary & 0xFF.
Byte reading macros implemented in library/common.h, All files
containing "& 0xff" were modified.
Comments/Documentation not yet added to the macro definitions.

Fixes #4274

Signed-off-by: Joe Subbiani <joe.subbiani@arm.com>
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index 626d137..b3b8e4c 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -245,8 +245,8 @@
     {
          goto cleanup;
     }
-    state_len_bytes[0] = ( clear_len >> 8 ) & 0xff;
-    state_len_bytes[1] = ( clear_len      ) & 0xff;
+    state_len_bytes[0] = BYTE_1( clear_len );
+    state_len_bytes[1] = BYTE_0( clear_len );
 
     /* Encrypt and authenticate */
     if( ( ret = mbedtls_cipher_auth_encrypt_ext( &key->ctx,