armv7: psci: make v7_flush_dcache_all public for all psci code

The v7_flush_dcache_all function will be called by ls102xa platform system
suspend, it is necessary to make it a public call instead of a local one, but
changing the LENTRY to ENTRY isn't enough, because there is another one using
the same name, so this one gets a psci_ prefix.

Signed-off-by: Hongbo Zhang <hongbo.zhang@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: York Sun <york.sun@nxp.com>