Wherever we use 'struct foo' and 'foo_t' interchangeably in a
function's declaration and definition, use 'struct foo' consistently
for both, as per the TF-A coding guidelines [1].

[1] https://github.com/ARM-software/arm-trusted-firmware/wiki/ARM-Trusted-Firmware-Coding-Guidelines#avoid-anonymous-typedefs-of-structsenums-in-header-files

Change-Id: I7998eb24a26746e87e9b6425529926406745b721
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>