Disconnect fasttrap from the 32-bit powerpc build.

An upcoming bug fix requires 64-bit atomics, which aren't implemented on
powerpc.  The powerpc port of fasttrap is incomplete anyway and doesn't
get loaded by dtraceall.ko on powerpc because of a missing dependency;
it's presumed that it's effectively unused.

Discussed with:	jhibbits
MFC after:	2 weeks

sys/modules/dtrace/Makefile

@@ -19,9 +19,6 @@ SUBDIR+=	fasttrap fbt systrace_linux
 .if ${MACHINE_CPUARCH} == "amd64"
 SUBDIR+=	systrace_linux32
 .endif
-.if ${MACHINE_CPUARCH} == "powerpc"
-SUBDIR+=	fbt fasttrap
-.endif
 .if ${MACHINE_CPUARCH} == "amd64" || \
     ${MACHINE_CPUARCH} == "aarch64" || \
     ${MACHINE_ARCH} == "mips64" || \
@@ -31,7 +28,9 @@ SUBDIR+=	systrace_freebsd32
 .if ${MACHINE_CPUARCH} == "aarch64" || \
     ${MACHINE_CPUARCH} == "arm" || \
     ${MACHINE_CPUARCH} == "mips" || \
+    ${MACHINE_CPUARCH} == "powerpc" || \
     ${MACHINE_CPUARCH} == "riscv"
 SUBDIR+=	fbt
 .endif
+
 .include <bsd.subdir.mk>