arm64: Expose ESR_EL1 information to user when SIGSEGV/SIGBUS

This information is useful for instruction emulators to detect
read/write and access size without having to decode the faulting
instruction. The current patch exports it via sigcontext (struct
esr_context) and is only valid for SIGSEGV and SIGBUS.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>