Follow other risc-v based chips, and fix:
```
chip/rv32m1_irq.c: In function 'up_irqinitialize':
Error: chip/rv32m1_irq.c:98:3: error: array subscript -2048 is outside array bounds of 'uint8_t[2147483647]' {aka 'unsigned char[2147483647]'} [-Werror=array-bounds]
98 | riscv_stack_color(g_intstacktop - intstack_size, intstack_size);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /github/workspace/sources/nuttx/arch/risc-v/src/common/riscv_internal.h:40,
from chip/rv32m1_irq.c:36:
/github/workspace/sources/nuttx/arch/risc-v/src/common/riscv_common_memorymap.h:72:16: note: at offset -2048 into object 'g_intstacktop' of size [0, 2147483647]
72 | EXTERN uint8_t g_intstacktop[]; /* Initial top of interrupt stack */
| ^~~~~~~~~~~~~
cc1: all warnings being treated as errors
```
Signed-off-by: Huang Qi <huangqi3@xiaomi.com>
74e59feaaa