ArmPkg/ArmScmiDxe: Dynamically allocate buffer for protocol ids

ArmPkg/ArmScmiDxe: Dynamically allocate buffer for protocol ids

Dynamically allocate the buffer to receive the SCMI protocol list.
This makes MAX_PROTOCOLS redundant, so it is removed.
It also fixes one minor code alignment issue and removes an unused
macro PROTOCOL_MASK.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Girish Pathak <girish.pathak@arm.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>