ta: rpc_test: fix trace messages specifiers

Use PRI* specifiers in trace messages using xMSG() macros.

Add parentheses to explicit function labels.

Remove function label from EMSG() trace messages as the macro already
takes care of printing it.

Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>