ARM: orion: always use MULTI_IRQ_HANDLER

As a preparation for multiplatform support, this enables
the MULTI_IRQ_HANDLER code unconditionally on dove and
orion5x, and introduces the respective code on mv78xx0,
which did not have it so far. The classic entry-macro.S
files are removed as they are now obsolete.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>