rpi3: fix bad formatting in rpi3.rst

d4fd0219 (pull request #1685) introduced unwanted formatting
such as bold/italic in the description for RPI3_USE_UEFI_MAP.

docs/plat/rpi3.rst

@@ -269,7 +269,6 @@ The following build options are supported:
     0x3F000000 +-----------------+
                |       I/O       |
 
-
 - ``BL32``: This port can load and run OP-TEE. The OP-TEE image is optional.
   Please use the code from `here <https://github.com/OP-TEE/optee_os>`__.
   Build the Trusted Firmware with option ``BL32=tee-header_v2.bin