Add support for software single step.

gdb:
	* epiphany-tdep.c (epiphany_is_instr32): Created.
	(epiphany_is_branch): Created.
	(epiphany_is_jump): Created.
	(epiphany_is_uncond_branch): Created.
	(epiphany_branch_offset): Created.
	(epiphany_jump_register): Created.
	(epiphany_ss_instr_type): Created.
	(epiphany_software_single_step): Created.
	(epiphany_gdbarch_init): Add software single step to arch.