replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

Add seL4_UserTop and move kernelBase to the arch level

- seL4_UserTop is a new constant which represents the top of virtual
memory available to user level
- this commit also rationalises several constants (USER_TOP, kernelBase)
and moves them to the arch level, such that ports only need to define
seL4_UserTop.

libsel4: fix licenses

- some were incorrectly marked GPL (libsel4 is BSD)
- update NICTA --> DATA61 etc
- fix tags D61 --> DATA61
- update year to 2017

SELFOUR-836: arm-hyp: Config option for saving/loading vs trapping debug state

Provides a configuration option for enabling HDCR.TD* traps, or saving and loading debug
state on VCPU switches. Currently verification only plans to support the trap setting.

As this option complicates all of the #ifdef's related to debug registers even further,
abstractions for enabling/disabling each individual piece of the debug code for different
configuration options are also implemented.

Part of these refactored #ifdef guards was to remove the guards completely from libsel4
around the definitions of the number of breakpoints and watchpoints.

SELFOUR-836: Disable debug context save/restore between VMs

This patch disables the debug register state save and restore on ARM-hyp,
such that Guest VMs can now interfere with one another and trigger
one another for certain limited scenarios. This will be undone later on.

ARM-HYP: Add support for save/restore of debug registers

As things are now, the Guest VMs can modify the debug registers at will
from non-secure PL1, and the kernel does nothing to ensure that guest VM
debug coprocessor registers are preserved.

This is a preliminary patch that simply hooks into vcpu_save and saves the
CPU's debug coprocessor registers when saving VCPU state.

For restoring the debug registers on switching to a VCPU, we just re-use
restore_user_debug_context, which is already called in restore_user_context.
(Restore_user_context is called by c_handle_vcpu_fault()). Specifically,
we modify the used_breakpoints_bf so that restore_user_debug_context()
will always pop all the debug context.

This patch only covers the breakpoint and watchpoint registers,
and it doesn't cover the entire debug coprocessor, which is another
conversation.

s/D61/DATA61/ in license headers for consistency

Replace #pragma once with include guards

SELFOUR-499: X86, ARM: Add userspace invocations for hardware debugging

This commit implements the body of SELFOUR-499. The API exposes the x86 DR0-7
and ARM coprocessor 14 features to userspace by virtualizing them as context-
switched registers in the TCB. Implemented as TCB invocations. This feature is
only built when CONFIG_HARDWARE_DEBUG_API is selected.

* Add low-level support routines for setting, unsetting, getting, enabling
and disabling breakpoints.
* Add support for single-stepping as well.
^ Single-stepping is not supported on ARMv6 since the hardware
doesn't have support.
^ ARM implements single-stepping as instruction breakpoints
configured to fault on every instruction -- this is achieved through
the "mismatch" mode, which is only supported from ARMv7 onwards.
* Also support explicit software break requests, a la "BKPT" and "INT $3".

* New invocations:
* seL4_TCB_SetBreakpoint().
* seL4_TCB_GetBreakpoint().
* seL4_TCB_UnsetBreakpoint().
* seL4_TCB_ConfigureSingleStepping().
* New constants:
^ Event types:
^ seL4_InstructionBreakpoint.
^ seL4_DataBreakpoint.
^ seL4_SoftwareBreakRequest.
^ Access types:
^ seL4_BreakOnRead.
^ seL4_BreakOnWrite.
^ seL4_BreakOnReadWrite.
^ Exports:
^ seL4_NumHWBreakpoints.
^ seL4_NumExclusiveBreakpoints.
^ seL4_NumExclusiveWatchpoints.
^ seL4_NumDualFunctionMonitors.
^ seL4_FirstBreakpoint.
^ seL4_FirstWatchpoint.
^ seL4_FirstDualFunctionMonitor.

See documentation in the seL4 API manual.