refactor(hisilicon): console runtime switch on bl31 exit

TF-A plans to move the console_flush() and
console_switch_state(CONOSLE_FLAG_RUNTIME) calls to bl31_main() just
before BL31 exits.

For now we are mimicking the generic implementation by calling flush
and changing the console state to runtime at the end of
bl31_plat_runtime_setup() for each platform. This is so that each
platform can test it prior to moving flush and switch to bl31_main().

This patch affects the Hisilicon SoCs (poplar, hikey, hikey960).

Change-Id: I0cbb0644377f663e880310362abb4308e24f0cef
Signed-off-by: Salman Nabi <salman.nabi@arm.com>
3 files changed