riscv: head: remove useless __PAGE_ALIGNED_BSS and .balign

After commit 83e7b876 ("RISC-V: move empty_zero_page definition to
C and export it"), the empty_zero_page has been moved outside head.S,
the __PAGE_ALIGNED_BSS and .balign LoCs are useless, clean up them.
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/head.S

@@ -447,7 +447,3 @@ ENTRY(reset_regs)
 	ret
 END(reset_regs)
 #endif /* CONFIG_RISCV_M_MODE */
-
-__PAGE_ALIGNED_BSS
-	/* Empty zero page */
-	.balign PAGE_SIZE