x86: Rename pcat_ to i8254 and i8259 accordingly

Rename pcat_timer.c to i8254.c and pcat_interrupts.c to i8259.c,
to match their header file names (i8254.h and i8259.h).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/interrupts.c b/arch/x86/cpu/interrupts.c
index addd26e..b00ddc0 100644
--- a/arch/x86/cpu/interrupts.c
+++ b/arch/x86/cpu/interrupts.c
@@ -252,7 +252,7 @@
 	/* Just in case... */
 	disable_interrupts();
 
-#ifdef CONFIG_SYS_PCAT_INTERRUPTS
+#ifdef CONFIG_I8259_PIC
 	/* Initialize the master/slave i8259 pic */
 	i8259_init();
 #endif