powerpc/fsl: Add macro to flush the branch predictor

BugLink: https://bugs.launchpad.net/bugs/1830176

commit 1cbf8990 upstream.

The BUCSR register can be used to invalidate the entries in the
branch prediction mechanisms.
Signed-off-by: Diana Craciun <diana.craciun@nxp.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/powerpc/include/asm/ppc_asm.h

@@ -821,4 +821,15 @@ END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,945)
 	.long 0x2400004c  /* rfid				*/
 #endif /* !CONFIG_PPC_BOOK3E */
 #endif /*  __ASSEMBLY__ */
+
+#ifdef CONFIG_PPC_FSL_BOOK3E
+#define BTB_FLUSH(reg)			\
+	lis reg,BUCSR_INIT@h;		\
+	ori reg,reg,BUCSR_INIT@l;	\
+	mtspr SPRN_BUCSR,reg;		\
+	isync;
+#else
+#define BTB_FLUSH(reg)
+#endif /* CONFIG_PPC_FSL_BOOK3E */
+
 #endif /* _ASM_POWERPC_PPC_ASM_H */