hw/xtensa: remove extraneous xtensa_ prefix from file names

While at it rename lx60 (named after the first board of the family) to
more generic xtfpga (the family name).

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

hw/xtensa/Makefile.objs

@@ -1,3 +1,3 @@
 obj-y += pic_cpu.o
-obj-y += xtensa_sim.o
-obj-y += xtensa_lx60.o
+obj-y += sim.o
+obj-y += xtfpga.o

hw/xtensa/xtfpga.c

@@ -37,7 +37,7 @@
 #include "hw/block/flash.h"
 #include "sysemu/blockdev.h"
 #include "sysemu/char.h"
-#include "xtensa_bootparam.h"
+#include "bootparam.h"
 
 typedef struct LxBoardDesc {
     hwaddr flash_base;