GCC: ARM_CM0: Fix L6286E error on Keil MDK (#1131)

Change the .b instruction to .bx with higher range to solve error
reported by MDK descibed bellow.

Fix:
Error: L6286E: Relocation #REL:0 in portasm.o(.text.SVC_Handler) with respect to vPortSVCHandler_C. Value(0x1a04) out of range(-0x800 - 0x7fe) for (R_ARM_THM_JUMP11)

Compiler: Keil MDK ARMClang 6.22.0

https://developer.arm.com/documentation/ka002847/latest/
https://developer.arm.com/documentation/dui0496/m/Linker-Errors-and-Warnings/List-of-the-armlink-error-and-warning-messages

Signed-off-by: Tomas Galbicka <tomas.galbicka@nxp.com>

portable/GCC/ARM_CM0/portasm.c

@@ -472,7 +472,8 @@ void vClearInterruptMask( __attribute__( ( unused ) ) uint32_t ulMask ) /* __att
             "     ldr r3, =%1                \n"
             "     cmp r2, r3                 \n"
             "     beq system_call_exit       \n"
-            "     b vPortSVCHandler_C        \n"
+            "     ldr r3, =vPortSVCHandler_C \n"
+            "     bx r3                      \n"
             "                                \n"
             " system_call_enter:             \n"
             "    push {lr}                   \n"
@@ -508,11 +509,13 @@ void vClearInterruptMask( __attribute__( ( unused ) ) uint32_t ulMask ) /* __att
             "                                \n"
             " stacking_used_psp:             \n"
             "    mrs r0, psp                 \n"
-            "    b vPortSVCHandler_C         \n"
+            "    ldr r3, =vPortSVCHandler_C  \n"
+            "    bx r3                       \n"
             "                                \n"
             " stacking_used_msp:             \n"
             "    mrs r0, msp                 \n"
-            "    b vPortSVCHandler_C         \n"
+            "    ldr r3, =vPortSVCHandler_C  \n"
+            "    bx r3                       \n"
             "                                \n"
             " .align 4                       \n"
         );