allwinner: doc: add missing paragraphs

Add two empty lines to denote the paragraphs properly and improve
readability.

Reported-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/docs/plat/allwinner.rst b/docs/plat/allwinner.rst
index a10e6dc..825fded 100644
--- a/docs/plat/allwinner.rst
+++ b/docs/plat/allwinner.rst
@@ -4,9 +4,11 @@
 Trusted Firmware-A (TF-A) implements the EL3 firmware layer for Allwinner
 SoCs with ARMv8 cores. Only BL31 is used to provide proper EL3 setup and
 PSCI runtime services.
+
 U-Boot's SPL acts as a loader, loading both BL31 and BL33 (typically U-Boot).
 Loading is done from SD card, eMMC or SPI flash, also via an USB debug
 interface (FEL).
+
 BL31 lives in SRAM A2, which is documented to be accessible from secure
 world only.