kgdb,arm: use macro in arch_kgdb_breakpoint

Replace hardcoded hexadecimal breakpoint value in arch_kgdb_breakpoint() by the
KGDB_COMPILED_BREAK macro, stringified.

Signed-off-by: Vincent Stehlé <v-stehle@ti.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: kgdb-bugreport@lists.sourceforge.net
WIP kgdb,arm: use macro in arch_kgdb_ops

Use a macro to deal with endianness while declaring breakpoint instruction in
arch_kgdb_ops, and refer the KGDB_BREAKINST macro instead of hardcoding the
breakpoint instruction in hexadecimal.

Signed-off-by: Vincent Stehlé <v-stehle@ti.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: kgdb-bugreport@lists.sourceforge.net

TODO
----
- Check if there exists a __bpt_byte-like macro already.
WIP kgdb,arm: add support for thumb2 kernel

Add breakpoint instructions for thumb2 kernel. This repairs the following
error:

  SysRq : DEBUG
  Internal error: Oops - undefined instruction: 0 [#1] SMP THUMB2

...and allows to enter kdb properly under thumb2 kernel for example.

Signed-off-by: Vincent Stehlé <v-stehle@ti.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: kgdb-bugreport@lists.sourceforge.net

Changes in v2:
- Add thumb2 32b breakpoints.

TODO
----
- We cannot have a 16b break in arch_kgdb_ops. Investigate consequences...