build-baremetal: enable parallel build and target selection just like build-userland

The factoring out also led to some small bugs being found and solved ;-)

baremetal/arch/arm/dump_regs.c

@@ -5,7 +5,7 @@
 
 int main(void) {
     uint32_t cpsr;
-    uint32_t mvfr1;
+    /*uint32_t mvfr1;*/
     __asm__ ("mrs %0, cpsr" : "=r" (cpsr) : :);
     /* TODO this is blowing up an exception, how to I read from it? */
     /*__asm__ ("vmrs %0, mvfr1" : "=r" (mvfr1) : :);*/

baremetal/arch/arm/multicore.S

@@ -19,7 +19,7 @@ cpu1_sleep_forever:
     wfe
     b cpu1_sleep_forever
 cpu0_only:
-#if !defined(GEM5)
+#if !LKMC_GEM5
     /* PSCI CPU_ON. */
     ldr r0, =0x84000003
     mov r1, #1