ARM/FDPIC: Add GDB support

ARM/FDPIC: Add GDB support

This patch mainly adds gdb/solib-fdpic.c which is based upon
solib-dsbt.c and solib-frv.c

2021-04-14  Mickael Guene  <mickael.guene@st.com>
	Christophe Lyon  <christophe.lyon@st.com>

	* gdb/Makefile.in: Add solib-fdpic.o to ALL_TARGET_OBS.
	* gdb/arm-linux-tdep.c (arm_linux_init_abi): Initialize FDPIC
	handlers.
	* gdb/arm-tdep.c (arm_gdbarch_init): Initialize is_fdpic as
	needed.
	* gdb/arm-tdep.h (gdbarch_tdep): Add is_fdpic field.
	(fdpic_so_ops, fdpic_fetch_objfile_link_map): Declare.
	* gdb/configure.tgt: Add solib-fdpic.o to gdb_target_obs.
	* gdb/solib-fdpic.c: New file.
	* include/elf/arm.h (EF_ARM_FDPIC): New define.