[ARM] arm64: Reorganize and modularize code

This patch make arm64 more modular by adding new modules
such as:
cpu_vcpu_vfp     - VCPU VFP emulation
cpu_vcpu_excep   - VCPU exception handling
cpu_vcpu_inject  - VCPU exception injection
cpu_vcpu_sysregs - VCPU sysreg, cp15, and cp14 emulation

The old cpu_vcpu_spr has been depricated from arm64 because
"spr" does not mean anything for arm64 hence cpu_vcpu_sysregs
replaces cpu_vcpu_spr.

Signed-off-by: Anup Patel <anup@brainfault.org>