elfloader: arm: fix potential UB in right shift

Regarding right shifts the standard says:

"The type of the result is that of the promoted left operand.
The behavior is undefined if the right operand is negative, or
greater than or equal to the length in bits of the promoted left
operand."

Corresponding GCC warning (if used on a "small" type like uint8_t):

main.c:25:39: warning: right shift count >= width of type
[-Wshift-count-overflow]

\#define GET_PGD_INDEX(x)        (((x) >> (ARM_2MB_BLOCK_BITS +
PMD_BITS + PUD_BITS)) & MASK(PGD_BITS))

main.c:46:39: note: in expansion of macro ‘GET_PGD_INDEX’
   46 |     printf("GET_PGD_INDEX(x): %lu\n", GET_PGD_INDEX(x));
      |                                       ^~~~~~~~~~~~~

Thus, make sure that we never exceed/reach it by explicitly casting
to a 64-bit type.

It also allows using a pointer as macro parameter.

This is a preparation patch for upcoming patches.

Signed-off-by: Matthias Rosenfelder <matthias.rosenfelder@nio.io>

elfloader-tool/include/arch-arm/64/mode/structures.h

@@ -21,9 +21,9 @@
 #define PMD_BITS                9
 #define PMD_SIZE_BITS           (PMD_BITS + PMDE_SIZE_BITS)
 
-#define GET_PGD_INDEX(x)        (((x) >> (ARM_2MB_BLOCK_BITS + PMD_BITS + PUD_BITS)) & MASK(PGD_BITS))
-#define GET_PUD_INDEX(x)        (((x) >> (ARM_2MB_BLOCK_BITS + PMD_BITS)) & MASK(PUD_BITS))
-#define GET_PMD_INDEX(x)        (((x) >> (ARM_2MB_BLOCK_BITS)) & MASK(PMD_BITS))
+#define GET_PGD_INDEX(x)        (((word_t)(x) >> (ARM_2MB_BLOCK_BITS + PMD_BITS + PUD_BITS)) & MASK(PGD_BITS))
+#define GET_PUD_INDEX(x)        (((word_t)(x) >> (ARM_2MB_BLOCK_BITS + PMD_BITS)) & MASK(PUD_BITS))
+#define GET_PMD_INDEX(x)        (((word_t)(x) >> (ARM_2MB_BLOCK_BITS)) & MASK(PMD_BITS))
 
 extern uint64_t _boot_pgd_up[BIT(PGD_BITS)];
 extern uint64_t _boot_pud_up[BIT(PUD_BITS)];