[PowerPC] Refactor have_ initializers in rs6000-tdep.c

[PowerPC] Refactor have_ initializers in rs6000-tdep.c

This patch refactors a series of initializers in rs6000_gdbarch_init
for clarity.  The have_fpu initializer is also changed to set the
variable to 0, like the other similar variables.  This doesn't affect
program behavior.

gdb/ChangeLog:
2018-10-26  Pedro Franco de Carvalho  <pedromfc@linux.ibm.com>

	* rs6000-tdep.c (rs6000_gdbarch_init): Replace line wrapping by a
	second initializer line for the have_* variables.  Initialize
	have_fpu to 0 instead of 1.