arm64: Reduce the number of header files pulled into vmlinux.lds.S

Although vmlinux.lds.S smells like an assembly file and is compiled
with __ASSEMBLY__ defined, it's actually just fed to the preprocessor to
create our linker script. This means that any assembly macros defined
by headers that it includes will result in a helpful link error:

| aarch64-linux-gnu-ld:./arch/arm64/kernel/vmlinux.lds:1: syntax error

In preparation for an arm64-private asm/rwonce.h implementation, which
will end up pulling assembly macros into linux/compiler.h, reduce the
number of headers we include directly and transitively in vmlinux.lds.S

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>