Introduce helper_get_dr so that we don't have to put CR4[DE]
into the scarce HFLAGS resource. At the same time, rename
helper_movl_drN_T0 to helper_set_dr and set the helper flags.
Backports commit d0052339236072bbf08c1d600c0906126b1ab258 from qemu
If the debug register is not enabled, we need
do nothing besides update the register.
Backports commit 7525b55051277717329cf64a9e1d5cff840d6f38 from qemu
Before the last patch, we had an efficient loop that disabled
local breakpoints on task switch. Re-add that, but in a more
general way that handles changes to the global enable bits too.
Backports commit 36eb6e096729f9aade3a6af7dbe4d0a990335d7e from qemu
This moves the last of the iteration over breakpoints into
the bpt_helper.c file. This also allows us to make several
breakpoint functions static.
Backports commit 93d00d0fbe4711061834730fb70525d167b6f908 from qemu
