ARM: simplify ARMv7-A register handling

ARM: simplify ARMv7-A register handling

ARMv7-A doesn't need to duplicate all the standard ARM code
for register handling.

 - Switch Cortex-A8 to use the standard register code
 - Remove duplicated infrastructure from ARMv7-A
 - Have ARMv7-A arch_state() show CPSR, like other ARMs

Add comments to show where the Cortex-A8 isn't actually doing
the right thing for register reads/writes, unless core happens
to be in the right mode to start with.  (Looks like maybe there
may be generic confusion between saved/current PSR values in all
the ARM code ...)

Make related ARMv7-A and Cortex-A8 symbols properly static.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>