Minor changes to documentation and comments

Fix some typos and clarify some sentences.

Change-Id: Id276d1ced9a991b4eddc5c47ad9a825e6b29ef74
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/lib/el3_runtime/aarch64/context.S b/lib/el3_runtime/aarch64/context.S
index 4489e90..4371cb2 100644
--- a/lib/el3_runtime/aarch64/context.S
+++ b/lib/el3_runtime/aarch64/context.S
@@ -456,7 +456,7 @@
 endfunc restore_gp_registers
 
 /* -----------------------------------------------------
- * Restore general purpose registers (including x30), and exit EL3 via. ERET to
+ * Restore general purpose registers (including x30), and exit EL3 via ERET to
  * a lower exception level.
  * -----------------------------------------------------
  */