Change the { } expression in tablegen to accept sized binary literals which are not just 0 and 1.

It also allows nested { } expressions, as now that they are sized, we can merge pull bits from the nested value.

In the current behaviour, everything in { } must have been convertible to a single bit.
However, now that binary literals are sized, its useful to be able to initialize a range of bits.

So, for example, its now possible to do

bits<8> x = { 0, 1, { 0b1001 }, 0, 0b0 }

llvm-svn: 215086