Rename GPIO_BITBAND to reflect its true capabilities

I was looking at the memory map, and realized that the peripheral
bitbanding region actually works for all peripherals, not just the GPIO
module.

Change-Id: I75b848732354106c1bea0f19c8cef970b304fd74
diff --git a/motors/util.h b/motors/util.h
index d1eaf53..458cf20 100644
--- a/motors/util.h
+++ b/motors/util.h
@@ -11,11 +11,11 @@
 {
 #endif
 
-// The GPIO bitband register for a specific bit of a given GPIO register.
+// This bitband register for a specific bit of a given peripheral register.
 //
-// reg really must be one of the GPIO module's addresses
-// (0x400FF000 - 0x400FFFFF).
-#define GPIO_BITBAND(reg, bit)                                             \
+// reg must be an address in one of the peripheral modules (on AIPS0, AIPS1, or
+// GPIO) (0x40000000 - 0x400FFFFF).
+#define PERIPHERAL_BITBAND(reg, bit)                                       \
   (*(volatile uint32_t *)(((uint32_t) & (reg)-0x40000000) * 32 + (bit)*4 + \
                           0x42000000))