video: fbdev: chipsfb: use memset_io() instead of memset()

While investigating a lockup at startup on Powerbook 3400C, it was
identified that the fbdev driver generates alignment exception at
startup:

  --- interrupt: 600 at memset+0x60/0xc0
  NIP:  c0021414 LR: c03fc49c CTR: 00007fff
  REGS: ca021c10 TRAP: 0600   Tainted: G        W          (5.14.2-pmac-00727-g12a41fa69492)
  MSR:  00009032 <EE,ME,IR,DR,RI>  CR: 44008442  XER: 20000100
  DAR: cab80020 DSISR: 00017c07
  GPR00: 00000007 ca021cd0 c14412e0 cab80000 00000000 00100000 cab8001c 00000004
  GPR08: 00100000 00007fff 00000000 00000000 84008442 00000000 c0006fb4 00000000
  GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00100000
  GPR24: 00000000 81800000 00000320 c15fa400 c14d1878 00000000 c14d1800 c094e19c
  NIP [c0021414] memset+0x60/0xc0
  LR [c03fc49c] chipsfb_pci_init+0x160/0x580
  --- interrupt: 600
  [ca021cd0] [c03fc46c] chipsfb_pci_init+0x130/0x580 (unreliable)
  [ca021d20] [c03a3a70] pci_device_probe+0xf8/0x1b8
  [ca021d50] [c043d584] really_probe.part.0+0xac/0x388
  [ca021d70] [c043d914] __driver_probe_device+0xb4/0x170
  [ca021d90] [c043da18] driver_probe_device+0x48/0x144
  [ca021dc0] [c043e318] __driver_attach+0x11c/0x1c4
  [ca021de0] [c043ad30] bus_for_each_dev+0x88/0xf0
  [ca021e10] [c043c724] bus_add_driver+0x190/0x22c
  [ca021e40] [c043ee94] driver_register+0x9c/0x170
  [ca021e60] [c0006c28] do_one_initcall+0x54/0x1ec
  [ca021ed0] [c08246e4] kernel_init_freeable+0x1c0/0x270
  [ca021f10] [c0006fdc] kernel_init+0x28/0x11c
  [ca021f30] [c0017148] ret_from_kernel_thread+0x14/0x1c
  Instruction dump:
  7d4601a4 39490777 7d4701a4 39490888 7d4801a4 39490999 7d4901a4 39290aaa
  7d2a01a4 4c00012c 4bfffe88 0fe00000 <4bfffe80> 9421fff0 38210010 48001970

This is due to 'dcbz' instruction being used on non-cached memory.
'dcbz' instruction is used by memset() to zeroize a complete
cacheline at once, and memset() is not expected to be used on non
cached memory.

When performing a 'sparse' check on fbdev driver, it also appears
that the use of memset() is unexpected:

  drivers/video/fbdev/chipsfb.c:334:17: warning: incorrect type in argument 1 (different address spaces)
  drivers/video/fbdev/chipsfb.c:334:17:    expected void *
  drivers/video/fbdev/chipsfb.c:334:17:    got char [noderef] __iomem *screen_base
  drivers/video/fbdev/chipsfb.c:334:15: warning: memset with byte count of 1048576

Use fb_memset() instead of memset(). fb_memset() is defined as
memset_io() for powerpc.

Fixes: 8c870933 ("[PATCH] ppc32: Remove CONFIG_PMAC_PBOOK")
Reported-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/884a54f1e5cb774c1d9b4db780209bee5d4f6718.1631712563.git.christophe.leroy@csgroup.eu

drivers/video/fbdev/chipsfb.c

@@ -331,7 +331,7 @@ static const struct fb_var_screeninfo chipsfb_var = {
 
 static void init_chips(struct fb_info *p, unsigned long addr)
 {
-	memset(p->screen_base, 0, 0x100000);
+	fb_memset(p->screen_base, 0, 0x100000);
 
 	p->fix = chipsfb_fix;
 	p->fix.smem_start = addr;