tm4c: add coreclock demo

Records the process of changing the CPU clock speed on various boards.

Note that TM4C123 devices incorrectly determine the current clock speed
on some versions of TivaWare; a patch for this may be necessary per
discussion culiminating in:
http://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/p/330524/1156581.aspx#1156581
Makefile.common: change to true dependency on generated archives

The order-only dependency almost works, but fails to update the
executable if a source file affecting an archive causes the archive to
be rebuilt.
utility/misc: add module

Add some functions to display memory contents on the console.
tm4c/button: display button port assignments
core: support aligned object definitions

Need this for the DMA channel control structure.
core: provide standard mechanism to set nybble in word

This moves the EFM32 function up into core.  For EFM32 the API uses two
consecutive words each of which packs 8 values into nybbles; these
correspond to nybble-values indexed by a GPIO pin.

TM4C also needs this functionality, but using a 5-bit DMA channel to
index a source selection nybble, so generalize the function.
tm4c/dma: add example
core: provide function to map from bit mask to bit number

TM4C device headers provide macro values for things like interrupt event
bits, for which we probably want the bit number so we can efficiently
set/clear the interrupt.
misc/bitband: add example
tm4c/spi: extend to ek-tm4c1294xl BP1 and BP2
core: use parallel constructs to make word/nybble indexing more clear
tm4c/gpio: clean up pinmux configuration

Add an example to probe behavior.  Experimentation shows that for
non-GPIO configurations there is no ability to set the initial output
state (e.g. to set TX high) so remove the unused parameter.  Document
that for GPIO configurations enable/disable reflects output/input state,
and change so for alternate function configurations enable/disable
actually enables and disables (rather than returning to GPIO input).
tm4c/multipulsetime: add demonstration

More a utility than an example, so it's not public domain.  This
measures, to microsecond resolution, the width of a series of pulses,
e.g. corresponding to an OOK-encoded RF signal.
Update for release