[efi] Add support for R_ARM_REL32 relocations

The relocation type R_ARM_REL32 is generated when building
bin-arm32-efi/snp.efi using gcc 6.3 and ld 2.28.

R_ARM_REL32 is a program counter (PC) relative 32 bit relocation so we
can ignore it like all other PC relative relocations.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/util/elf2efi.c

 			break;
 		case ELF_MREL ( EM_386, R_386_PC32 ) :
 		case ELF_MREL ( EM_ARM, R_ARM_CALL ) :
+		case ELF_MREL ( EM_ARM, R_ARM_REL32 ) :
 		case ELF_MREL ( EM_ARM, R_ARM_THM_PC22 ) :
 		case ELF_MREL ( EM_ARM, R_ARM_THM_JUMP24 ) :
 		case ELF_MREL ( EM_ARM, R_ARM_V4BX ):