arm64 hitting BUG in arch_timer.h

[Mark Salter]

Using Linus' tree from this morning, I am hitting:

   [    0.000000] BUG: failure at ./arch/arm64/include/asm/arch_timer.h:112/arch_counter_get_cntpct!

This is triggered by commit 0b46b8a718 ("clocksource: arch_timer: Fix
code to use physical timers when requested") which addresses an armv7
problem. Arm64 wants to always use a virtual timer. I used this to avoid
the BUG and get a booting kernel:

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch
index 71846f9..4d8a01e 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -468,7 +468,7 @@ static void __init arch_counter_register(unsigned type)
 
        /* Register the CP15 based counter if we have one */
        if (type & ARCH_CP15_TIMER) {
-               if (arch_timer_use_virtual)
+               if (IS_ENABLED(CONFIG_ARM64) || arch_timer_use_virtual)
                        arch_timer_read_counter = arch_counter_get_cntvct;
                else
                        arch_timer_read_counter = arch_counter_get_cntpct;