Kernel: Heap alignment bug

[sohshri796-cell]

There's a bug when allocating memory in heap.c.
The memory we allocated wasnt aligned as the mcu needs it to be. So i modified the file to allocate the memory in only multiples of 8. So it allocates memory interms of nearest higher multiple of 8.
This needs to be done as without proper alignment if user asks for some memory which isnt multiple of 4, the cpu stalls due to unaligned memory access.
It allocates memory in multiples of 8 rather than in 4's is because if we ever need other data types like double which need more than 4 bytes of space.

I tested this using this code snippet:

#include "system_init.h"
#include "uart.h"
#include "task.h"
#include "heap.h"

void task(void){
while(1){
uart_send_string(USART1_BASE, "TASK IS RUNNING\r\n");
    }
}

int main(){
system_init();
uart_init(USART1_BASE);
systick_init();
os_heap_init();
os_task_create(task, 2, 129);
os_malloc(13);
os_malloc(7);
os_start();
return 0;
}

when we run this without proper alignment in memory it would just stall.
I tested this on both hardware as well as QEMU.

[vedantmalkar]

LGTM