MdeModulePkg VarCheck: #### in L"Boot####" are upper case hex

MdeModulePkg VarCheck: #### in L"Boot####" are upper case hex

UEFI spec:
Each load option entry resides in a Boot####, Driver####, SysPrep####,
OsRecovery#### or PlatformRecovery#### variable where #### is replaced
by a unique option number in printable hexadecimal representation using
the digits 0-9, and the upper case versions of the characters A-F
(0000-FFFF).

The patch also makes L"HwErrRec####" follow this rule.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>