riscv: remove breakpoint_stack from linker script

Presumably, this was copied from the common_arm.lds linker script,
but it was a particular implementation detail of the arm32 code,
and is unneeded on RISC-V.

Signed-off-by: julia <git.ts@trainwit.ch>

src/arch/riscv/common_riscv.lds

@@ -87,11 +87,6 @@ SECTIONS
         *(.bss)
         *(COMMON) /* fallback in case '-fno-common' is not used */
 
-        /* 4k breakpoint stack */
-        _breakpoint_stack_bottom = .;
-        . = . + 4K;
-        _breakpoint_stack_top = .;
-
         /* large data such as the globals frame and global PD */
         *(.bss.aligned)
 #if defined(CONFIG_PLAT_ROCKETCHIP_ZCU102)