powerpc/kasan: Disable KCOV in KASAN code

As per the generic KASAN code in mm/kasan, disable KCOV with
KCOV_INSTRUMENT := n in the makefile.

This fixes a ppc64 boot hang when KCOV and KASAN are enabled.
kasan_early_init() gets called before a PACA is initialised, but the
KCOV hook expects a valid PACA.
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230710044143.146840-1-bgray@linux.ibm.com

arch/powerpc/mm/kasan/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
 KASAN_SANITIZE := n
+KCOV_INSTRUMENT := n
 
 obj-$(CONFIG_PPC32)		+= init_32.o
 obj-$(CONFIG_PPC_8xx)		+= 8xx.o