arch: riscv: Use CONFIG_PMP_SLOTS for PMP array sizing

The arrays used for M-mode Physical Memory Protection (PMP),
specifically for the stack guard feature (CONFIG_PMP_STACK_GUARD),
were previously sized using the hardcoded PMP_M_MODE_SLOTS macro,
defined as 8. This affected arrays in both the _thread_arch
struct (m_mode_pmpaddr_regs, m_mode_pmpcfg_regs) and local
variables within the z_riscv_pmp_stackguard_disable function.

This commit changes the array sizing to use the Kconfig option
CONFIG_PMP_SLOTS. This option reflects the total number of PMP
slots available and configured for the target hardware.

Using CONFIG_PMP_SLOTS ensures these arrays are dimensioned
according to the system's actual capabilities, providing better
flexibility and correctness over a fixed size.

The PMP_M_MODE_SLOTS macro definition has been removed from
thread.h as it is no longer used.

Signed-off-by: Firas Sammoura <[email protected]>

Author: fsammoura1980

arch/riscv/core/pmp.c

@@ -539,8 +539,8 @@ void z_riscv_pmp_stackguard_enable(struct k_thread *thread)
 void z_riscv_pmp_stackguard_disable(void)
 {
 
-	unsigned long pmp_addr[PMP_M_MODE_SLOTS];
-	unsigned long pmp_cfg[PMP_M_MODE_SLOTS / sizeof(unsigned long)];
+	unsigned long pmp_addr[CONFIG_PMP_SLOTS];
+	unsigned long pmp_cfg[CONFIG_PMP_SLOTS / sizeof(unsigned long)];
 	unsigned int index = global_pmp_end_index;
 
 	/* Retrieve the pmpaddr value matching the last global PMP slot. */

include/zephyr/arch/riscv/thread.h

@@ -63,8 +63,6 @@ struct z_riscv_fp_context {
 };
 typedef struct z_riscv_fp_context z_riscv_fp_context_t;
 
-#define PMP_M_MODE_SLOTS 8	/* 8 is plenty enough for m-mode */
-
 struct _thread_arch {
 #ifdef CONFIG_FPU_SHARING
 	struct z_riscv_fp_context saved_fp_context;
@@ -81,8 +79,8 @@ struct _thread_arch {
 #endif
 #ifdef CONFIG_PMP_STACK_GUARD
 	unsigned int m_mode_pmp_end_index;
-	unsigned long m_mode_pmpaddr_regs[PMP_M_MODE_SLOTS];
-	unsigned long m_mode_pmpcfg_regs[PMP_M_MODE_SLOTS / sizeof(unsigned long)];
+	unsigned long m_mode_pmpaddr_regs[CONFIG_PMP_SLOTS];
+	unsigned long m_mode_pmpcfg_regs[CONFIG_PMP_SLOTS / sizeof(unsigned long)];
 #endif
 };