mediatek: mt7623: Re-enable ARM arch timer

CONFIG_ARM_ARCH_TIMER cannot be enabled in the config directly; it is only
selected by CONFIG_HAVE_ARM_ARCH_TIMER. We need to enable the latter in
our config.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Fixes: 4f1c5b0 ("mediatek: mt7623: backport musb, improve HDMI console")

target/linux/mediatek/mt7623/config-5.10

@@ -260,6 +260,7 @@ CONFIG_HARDIRQS_SW_RESEND=y
 CONFIG_HAS_DMA=y
 CONFIG_HAS_IOMEM=y
 CONFIG_HAS_IOPORT_MAP=y
+CONFIG_HAVE_ARM_ARCH_TIMER=y
 CONFIG_HAVE_SMP=y
 CONFIG_HDMI=y
 CONFIG_HID=y