Simplify print_scalar_formatted

Simplify print_scalar_formatted

This unifies the two switches in print_scalar_formatted, removing some
now-redundant code.  Now scalar types are never converted to LONGEST,
instead printing is done using print_*_chars, operating on the byte
representation.

ChangeLog
2017-06-12  Tom Tromey  <tom@tromey.com>

	* printcmd.c (print_scalar_formatted): Unify the two switches.
	Don't convert scalars to LONGEST.

2017-06-12  Tom Tromey  <tom@tromey.com>

	* gdb.arch/altivec-regs.exp: Expect decimal results for uint128.