base: Add more bit utils and bit struct class

Allows efficient, zero-cost, bitwise memory storage.

 // Definition for type 'Example'
 BITSTRUCT_DEFINE_START(Example, 10)
   BitStructUint<0, 2> u2;     // Every field must be a BitStruct[*].
   BitStructInt<2, 7>  i7;
   BitStructUint<9, 1> i1;
 BITSTRUCT_DEFINE_END(Example);

 Would define a bit struct with this layout:
  <- 1 ->    <--  7  -->  <- 2 ->
 +--------+---------------+-----+
 |   i1   |       i7      | u2  +
 +--------+---------------+-----+
 10       9               2     0

See bit_struct.h for more documentation.

(Also adds new BitField[Extract|Insert|Clear] bit_utils similar
to the ARM bitfield instructions).

Test: art/test.py --gtest
Change-Id: I5e43f2468c5d275ee872546855527bb4ea73ad4c