EFI: Avoid crash calling PrintErrMesg from efi_multiboot2

EFI: Avoid crash calling PrintErrMesg from efi_multiboot2

Although code is compiled with -fpic option data is not position
independent. This causes data pointer to become invalid if
code is not relocated properly which is what happens for
efi_multiboot2 which is called by multiboot entry code.

Code tested adding
   PrintErrMesg(L"Test message", EFI_BUFFER_TOO_SMALL);
in efi_multiboot2 before calling efi_arch_edd (this function
can potentially call PrintErrMesg).

Before the patch (XenServer installation on Qemu, xen replaced
with vanilla xen.gz):
  Booting `XenServer (Serial)'Booting `XenServer (Serial)'
  Test message: !!!! X64 Exception Type - 0E(#PF - Page-Fault)  CPU Apic ID - 00000000 !!!!
  ExceptionData - 0000000000000000  I:0 R:0 U:0 W:0 P:0 PK:0 SS:0 SGX:0
  RIP  - 000000007EE21E9A, CS  - 0000000000000038, RFLAGS - 0000000000210246
  RAX  - 000000007FF0C1B5, RCX - 0000000000000050, RDX - 0000000000000010
  RBX  - 0000000000000000, RSP - 000000007FF0C180, RBP - 000000007FF0C210
  RSI  - FFFF82D040467CE8, RDI - 0000000000000000
  R8   - 000000007FF0C1C8, R9  - 000000007FF0C1C0, R10 - 0000000000000000
  R11  - 0000000000001020, R12 - FFFF82D040467CE8, R13 - 000000007FF0C1B8
  R14  - 000000007EA33328, R15 - 000000007EA332D8
  DS   - 0000000000000030, ES  - 0000000000000030, FS  - 0000000000000030
  GS   - 0000000000000030, SS  - 0000000000000030
  CR0  - 0000000080010033, CR2 - FFFF82D040467CE8, CR3 - 000000007FC01000
  CR4  - 0000000000000668, CR8 - 0000000000000000
  DR0  - 0000000000000000, DR1 - 0000000000000000, DR2 - 0000000000000000
  DR3  - 0000000000000000, DR6 - 00000000FFFF0FF0, DR7 - 0000000000000400
  GDTR - 000000007F9DB000 0000000000000047, LDTR - 0000000000000000
  IDTR - 000000007F48E018 0000000000000FFF,   TR - 0000000000000000
  FXSAVE_STATE - 000000007FF0BDE0
  !!!! Find image based on IP(0x7EE21E9A) (No PDB)  (ImageBase=000000007EE20000, EntryPoint=000000007EE23935) !!!!

After the patch:
  Booting `XenServer (Serial)'Booting `XenServer (Serial)'
  Test message: Buffer too small
  BdsDxe: loading Boot0000 "UiApp" from Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331)
  BdsDxe: starting Boot0000 "UiApp" from Fv(7CB8BDC9-F8EB-4F34-AAEA-3EE4AF6516A1)/FvFile(462CAA21-7614-4503-836E-8AB6F4662331)

This partially rollback commit 00d5d5ce23e6.

Fixes: 9180f5365524 ("x86: add multiboot2 protocol support for EFI platforms")
Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>