ofw_cpu: Make ext_resources non-optional for arm* and riscv

EXT_RESOURCES have been introduced in 12-CURRENT and all supported
releases have it enabled in their kernel config.
For RISC-V it was always enabled.

MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D33835

sys/dev/ofw/ofw_cpu.c

@@ -45,7 +45,7 @@ __FBSDID("$FreeBSD$");
 #include <dev/ofw/ofw_bus_subr.h>
 #include <dev/ofw/ofw_cpu.h>
 
-#ifdef EXT_RESOURCES
+#if defined(__arm__) || defined(__arm64__) || defined(__riscv__)
 #include <dev/extres/clk/clk.h>
 #endif
 
@@ -207,7 +207,7 @@ ofw_cpu_attach(device_t dev)
 	phandle_t node;
 	pcell_t cell;
 	int rv;
-#ifdef EXT_RESOURCES
+#if defined(__arm__) || defined(__arm64__) || defined(__riscv__)
 	clk_t cpuclk;
 	uint64_t freq;
 #endif
@@ -277,7 +277,7 @@ ofw_cpu_attach(device_t dev)
 	sc->sc_cpu_pcpu = pcpu_find(device_get_unit(dev));
 
 	if (OF_getencprop(node, "clock-frequency", &cell, sizeof(cell)) < 0) {
-#ifdef EXT_RESOURCES
+#if defined(__arm__) || defined(__arm64__) || defined(__riscv__)
 		rv = clk_get_by_ofw_index(dev, 0, 0, &cpuclk);
 		if (rv == 0) {
 			rv = clk_get_freq(cpuclk, &freq);