arm64: Fix missing #include in hw_breakpoint.c

A prior commit used to detect the hw breakpoint ABI behaviour based on
the target state missed the asm/compat.h include and the build fails
with !CONFIG_COMPAT.

Fixes: 8f48c062

 ("arm64: hw_breakpoint: use target state to determine ABI behaviour")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>