[ARM] Remove asm/arch/irq.h

asm/arch/irq.h used to be included from asm/irq.h, but was removed
from the ARM kernel a long time ago.  Consequently, the contents
of asm/arch/irq.h (which mostly contain a definition for fixup_irq())
have not been used.  Hence, remove asm/arch/irq.h.

Some machine support files incorrectly included this file, making
little or no use of the contents.  Move the contents to a local
include file, and remove those include statements as well.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>