[FREELDR] Improvements for the RamDisk support.

- Implement support for the "RDIMAGELENGTH" and "RDIMAGEOFFSET" boot
  options. Fixes CORE-15432.

- Separate the initialization of the global gInitRamDiskBase /
  gInitRamDiskSize variables from the FreeLdr command-line, and the
  actual initialization of the internal variables of the RamDisk.
  The latter are initialized via calls to RamDiskInitialize().

- Implement 'SeekRelative' mode in RamDiskSeek().

- Make RamDiskLoadVirtualFile() internal function that gets called by
  RamDiskInitialize(), and we use the latter in the NT loader instead.

Author: HBelusca

boot/freeldr/freeldr/arch/arm/macharm.c

@@ -120,8 +120,8 @@ ArmHwDetect(VOID)
     SecondLevelIcacheSize =
     SecondLevelIcacheFillSize = 0;
 
-    /* Register RAMDISK Device */
-    RamDiskInitialize();
+    /* Initialize the RAMDISK Device */
+    RamDiskInitialize(TRUE, NULL, NULL);
 
     /* Fill out the ARC disk block */
     AddReactOSArcDiskInfo("ramdisk(0)", 0xBADAB00F, 0xDEADBABE, TRUE);

boot/freeldr/freeldr/cmdline.c

@@ -91,7 +91,7 @@ CmdLineParse(IN PCSTR CmdLine)
     Setting = strstr(CmdLine, "rdbase=");
     if (Setting)
     {
-        gRamDiskBase =
+        gInitRamDiskBase =
             (PVOID)(ULONG_PTR)strtoull(Setting +
                                        sizeof("rdbase=") - sizeof(ANSI_NULL),
                                        NULL, 0);
@@ -101,9 +101,9 @@ CmdLineParse(IN PCSTR CmdLine)
     Setting = strstr(CmdLine, "rdsize=");
     if (Setting)
     {
-        gRamDiskSize = strtoul(Setting +
-                               sizeof("rdsize=") - sizeof(ANSI_NULL),
-                               NULL, 0);
+        gInitRamDiskSize = strtoul(Setting +
+                                   sizeof("rdsize=") - sizeof(ANSI_NULL),
+                                   NULL, 0);
     }
 
     /* Get ramdisk offset */
@@ -116,7 +116,7 @@ CmdLineParse(IN PCSTR CmdLine)
     }
 
     /* Fix it up */
-    gRamDiskBase = (PVOID)((ULONG_PTR)gRamDiskBase + Offset);
+    gInitRamDiskBase = (PVOID)((ULONG_PTR)gInitRamDiskBase + Offset);
 }
 
 PCSTR