hv: replace MEM_2K with a new macro MAX_BOOTARGS_SIZE for bootargs size

- for all cases of referring guest bootargs size, replace MEM_2K with
  CONFIG_MAX_BOOTARGS_SIZE for better readability.
- remove duplicated MAX_BOOTARGS_SIZE definition from vm_config.h.

Also fix one minor issue in general_sw_loader() which uses copy_to_gpa()
to copy a string. Since copy_to_gpa() makes use of memncpy_s() to do the
job, the size parameter should include the string null ternimator.

Tracked-On: #2806
Signed-off-by: Zide Chen <zide.chen@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/include/arch/x86/multiboot.h

@@ -14,6 +14,9 @@
 #define	MULTIBOOT_INFO_HAS_DRIVES	0x00000080U
 #define	MULTIBOOT_INFO_HAS_LOADER_NAME	0x00000200U
 
+/* maximum lengt of the guest OS' command line parameter string */
+#define MAX_BOOTARGS_SIZE		2048U
+
 struct acrn_vm;
 struct multiboot_info {
 	uint32_t               mi_flags;

hypervisor/include/arch/x86/vm_config.h

@@ -9,8 +9,8 @@
 
 #include <types.h>
 #include <pci.h>
+#include <multiboot.h>
 
-#define MAX_BOOTARGS_SIZE	1024U
 #define MAX_CONFIG_NAME_SIZE	32U
 
 #define PLUG_CPU(n)		(1U << (n))