powerpc/syscall: Rename syscall_64.c into interrupt.c

syscall_64.c will be reused almost as is for PPC32.

As this file also contains functions to handle other types
of interrupts rename it interrupt.c

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cddc2deaa8f049d3ec419738e69804934919b935.1612796617.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/Makefile

@@ -49,7 +49,7 @@ obj-y				:= cputable.o syscalls.o \
 				   hw_breakpoint_constraints.o
 obj-y				+= ptrace/
 obj-$(CONFIG_PPC64)		+= setup_64.o \
-				   paca.o nvram_64.o note.o syscall_64.o
+				   paca.o nvram_64.o note.o interrupt.o
 obj-$(CONFIG_COMPAT)		+= sys_ppc32.o signal_32.o
 obj-$(CONFIG_VDSO32)		+= vdso32/
 obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o