Unsigned long should not be used as per coding guidelines

We should either change them to `unsigned int` or `unsigned long long`
when the size of the variable is the same in AArch64 and AArch32 or
to `u_register_t` if it is supposed to be 32 bit wide in AArch32
and 64 bit wide in AArch64.

Signed-off-by: Deepika Bhavnani <deepika.bhavnani@arm.com>
Change-Id: I80e2a6edb33248ee88be395829abbd4c36c89abe